Thinking About Ob/Gyn
A fresh and evidence-based perspective of all things related to obstetrics and gynecology. Follow us on Instagram @thinkingaboutobgyn or visit thinkingaboutobgyn.com for show notes and more.
Thinking About Ob/Gyn
Episode 8.6 Cervical Catheters, SGA, Due Date Errors, History of Postpartum Depression
In this episode, we discuss four tips for placing and using catheters for induction of labor. Then we revisit the issue of small for gestational age versus fetal growth restriction. We also discuss the most common mistake made in calculating due dates and how this can have a negative impact on pregnancies. Finally, we discuss the history of postpartum depression and the literature and stories of Kate Chopin and Sylvia Plath.
00:00:35 Four Tips for Cervical Catheter Placement
00:23:00 SGA vs FGR
00:28:55 Correcting Due Dates Prevents Mistakes
00:46:10 History of Postpartum Depression, Chopin and Plath
Follow us on Instagram @thinkingaboutobgyn.
This is Thinking About OB-GYN with your hosts Antonia Roberts and Howard Harrell.
Speaker 2:Antonia.
Speaker 3:Howard.
Speaker 2:What are we thinking about on today's episode?
Speaker 3:Well, we're going to talk about some good for practical tips and then we're going to go back to some maybe smaller, nitpickier details about the fetal growth restriction discussion we just recently had, and hopefully we'll also get in some good historical tidbits.
Speaker 3:But first we'll start with some four tips, and that is inserting a balloon for cervical ripening. So using a balloon above the cervix during the ripening phase of a labor induction is probably the most evidence-based method of induction that we have and it's very effective, especially when it's coupled with mesoprostol or oxytocin at the same time. So this is a very bread and butter basic competency for any obstetric provider, but it can be tricky to do in some cases and tricky to learn as well. It's definitely not something you just hand to a med student on their first day with no instruction and say just go put it in the cervix, you'll be fine. So to my knowledge it's also not a nursing skill. It's never been anywhere that I've worked anyway, like maybe some other things could be, for example, an IUPC insertion. So our first tip here we actually mentioned this previously when we discussed value-based care and obstetrics and that is to use an inexpensive Foley catheter, the kind that's primarily designed for draining the bladder. Don't use the costly double balloon that was made for cervical ripening.
Speaker 2:Yeah, that's right and we discussed this back in episode 4.9 so many years ago. And the evidence does show clearly that the double balloon is no more effective than a single balloon at achieving vaginal delivery. They do so in about the same amount of time with about the same level of maternal satisfaction. But the Foley catheters are about the same level of maternal satisfaction. But the Foley catheters are just in the range of $1 to $2, $3. And the Cook catheter prices have come down. That's what happens when we don't use expensive products, is they lower the price? So they can be had in bulk now for $30, but that's still 10 times the cost and just no reason to use a more expensive catheter. And it's more cumbersome, more, frankly, takes longer to insert and you do want to use a 24 or 26 French catheter if you can, although sometimes it's probably useful to use a smaller one if the cervix is really open at all. But if you can get a 24 or 26, go for it.
Speaker 3:Okay. Our second tip has to do with making it easier to insert. I think the standard way most physicians insert this is just blindly with their hand, by feel, during an exam.
Speaker 2:Yeah, and I often think, if that's what you're doing, you're probably not inserting catheters into some of the patients who really need them the most, because if you can do that, the cervix is usually relatively anterior and maybe even half a centimeter or even two centimeters dilated, so that's fine. But that method for me, you're probably not putting them into the people who are a fingertip or closed and very posterior, and you may be not using catheters in some patients that you could be using them in and denying them this effective method of induction.
Speaker 3:Okay. So with this second tip to make the balloon easier to insert in those difficult cases, it's going to involve either using some kind of rigid item to help assist the floppy little catheter to go in, so either a swab or a pediatric intubation stylet. Because, as I mentioned, if the cervix is really long and firm and then you have this really soft catheter, you're not going to be able to force it inside the cervix and you just won't. You won't get it in. If they're already a centimeter or two dilated, it doesn't matter, it'll just pop right in and you can snake it through with your finger. But if they're very closed and firm, your finger can't do that. So I do a lot of these by feel honestly. And of course, if they're one centimeter dilated, I still think they'll probably get by faster with a Foley than without, even if it is easy to insert.
Speaker 3:But in those difficult cases I'll start by elevating the pelvis, either by having the patient lay on her fists or maybe using the bedpan, and that helps for those really posterior cervix positions. And then sometimes I'll also pre-medicate them with fentanyl, because the more posterior they are, the more uncomfortable this usually is. And then you could also use a speculum, and I definitely have colleagues that just use a speculum every single time. I'd say for me it's more of a last resort because I don't know if it's having skinny fingers, but I'm almost always able to stabilize the cervix, pull it way forward just with my hand and feed the Foley through. But it's good to have some other tricks up your sleeve.
Speaker 2:Yeah, so let's start with the idea of using a speculum first. So in multiparous patients, it probably doesn't make much of a difference. These are the ones where it's usually relatively easy to insert, and I'll put a link to a recent 2023 trial that showed that patients prefer not using the speculum. So if you can get by without it, it's a little more comfortable.
Speaker 2:So it's not something that you need to do for the easier patients, easier insertions. There's also a 2024 study that examined this in no leprous patients and they found again that there really wasn't much of a difference. There were failures in both groups, both the speculum versus a digital insertion group, but this study was probably underpowered to see a difference. There was a failure to place the catheter in 10.8% of the patients in the digital insertion group and 7.4% of the patients with the speculum. So that wasn't statistically significant given the power of their study. But they didn't use the rest of this tip, which is to then use something, as you said, to guide the catheter in. So you can use the non-business end of one of those large white Texas swabs Procta swabs that we all have on labor and delivery and you insert the end of that just into the little hole the urine comes out of at the end of the catheter and makes that easier to just push the tip through the cervix and you don't need a speculum to do that with. You can do it with a speculum or you can do it with your hand.
Speaker 2:Those failure rates from that study to me are unacceptably high and I don't fail to get it in 11% of the time, and I think they reveal the problem with not using something in those hard patients, at least rigid, to push the catheter through. Now that's what I typically do. I'll start with digital placement, but if it's very difficult or the cervix is closed or very posterior, then yeah, I'll switch to a speculum, and it's really essential to use something with a speculum, even more so to push the catheter through when you use a speculum, because you can't put your finger up there and you could use some ring forceps or something like that to try to push it up, but the ring forceps doesn't make the end of the catheter more rigid. So if you're going through a closed or fingertip cervix, you're probably not going to get it in there.
Speaker 2:Now, years ago I also used to routinely use a pediatric intubation stylet and so you feed the stylet into the actual tube of the Foley and you just work it all the way down to the tip and then you have to put a bend in it. So you know, because the stylet is rigid so that it prevents it from sliding back. But once you do that, then you can actually curve the end of the Foley into a nice gentle curve, if it's very posterior, to guide the direction of it and it won't slide back. And this makes it actually incredibly easy to insert these. I think if you're using a pediatric intubation stylet inside of it which I rarely, if ever do nowadays you can virtually place these in anyone because it just makes it rigid just like intubating somebody.
Speaker 2:But the downside is that once the catheter, the Foley, is in place in the cervix, well, you can't remove the stylet, it's just stuck in there. But I never saw that to make much of a difference. But I think you can achieve a much easier and higher success rates by using something rigid to guide the Foley in there, and if that doesn't work or if the patient's very uncomfortable, then a speculum plus. That, I think, gets these in almost everybody. So if you're not using something to make the catheter more rigid at the tip, that may be helpful, and you don't have to do that in every patient. You can have a process where you examine them and this is easy and put it in, or you recognize. No, this is very posterior and closed internally and I'm going to need some more help here, and then use one of those methods.
Speaker 3:We'll include pictures of what we're talking about here on our Instagram page that shows exactly how to use the swab or the stylet to make the Foley more rigid. But those big swabs and those pediatric intubation stylettes should be on every labor and delivery ward I think in the US, because we use those swabs a lot in triage and obviously the intubation materials for NRP as needed. So it's interesting that none of those trials have so far included a comparison of these techniques. Most trials just include women with Bishop scores of less than five, without any further breakdown, especially of where the failures occur. I would imagine they occur in people with a Bishop score of one or two or something like that, or zero.
Speaker 3:So those patients will end up often getting a prostaglandin without the Foley because the Foley placement was a failure. Maybe one of our listeners out there who might be research inclined, especially someone early in their training, could do a trial comparing stylet versus swab to guide in the Foley catheter and maybe demonstrate a lower failure rate with either of those compared with just straight digital or speculum placement. If you do that, make sure you include both of us as authors in that study, all right. Our next tip is fill the balloon catheter to 50 or 60 mLs, not 30 mLs.
Speaker 2:Yeah, 30 milliliters is all over the place and seems to be maybe what most people do most commonly or traditionally. It's what's in a lot of the textbooks or what was used in a lot of the initial studies that looked at efficacy and safety of this as a method of induction. But a lot of us have been using 50 or 60 mLs per year for years, and I'll put a link to a recent randomized trial that showed that this led to better outcomes with equal feasibility and tolerability by the patients. So the goal should actually be to put 50 or 60 mLs in and again probably to use concurrent oxytocin or mesoprostol when possible. I think people are worried about the catheters rupturing if you overfill them, but we'll put some pictures on the Instagram too, where we filled these catheters easily to about 150 milliliters before they ruptured.
Speaker 2:As you put more fluid in, the size of the bulb gets bigger. So with 30 mLs the balloon is just under four centimeters, but when it's actually in situ, of course it's going to be distorted a bit. It's probably a little bit smaller than that inside, but if you put 60 mLs in, it gets to 4.8 centimeters, and again that probably gets a little in. It gets to 4.8 centimeters and again, that probably gets a little compressed when it's squeezed against the cervix and is hourglassing. And I'll put a link to a study that has rigorously evaluated sort of the rupture rates. And these balloons typically rupture by 170 mLs but under 100 milliliters we rarely. You just don't, you don't see them rupture. So 60 mLs just isn't an issue and not a concern for rupture and likely leads to quicker vaginal delivery than 30 mLs does.
Speaker 3:And likely fewer cesareans.
Speaker 2:Yeah.
Speaker 3:I will say I don't think all Foley catheters out there are created equal. Obviously there's different sizes. I do remember one case many years ago that happened to a colleague's patient this was not at my current hospital where the balloon did rupture inside the patient's uterus and there was all the little fragments. I think that they had run out of the typical adult-sized foleys. Maybe they were using a pediatric foley, Maybe they were applying a ton of tension or pressure I don't recall the full details, but I know that it did rupture.
Speaker 3:It was more than 30 mLs and so after that the whole department had to strongly react and say no Foley will ever be inflated more than 30 mLs. At least the rest of the time I was there, that became the policy. I think these are designed. When you put them in the bladder you only have to inflate them to 10 CCs, and obviously we need more for the cervical ripening, but, as you said, it should hold more safely. So I think that maybe there's been a fluke out here or there where one of them broke, and maybe that's why we see 30 mLs a lot.
Speaker 2:Or if you're certainly using a really small catheter because they're closed or something, and you're trying to get an 18 or a 16 in there, yeah, maybe stick with 30. But if you're doing a 24 or 26, 60 is the way to go.
Speaker 3:Yeah, and it is clear that the cervical Foley plus Pitocin or Musoprostol is the preferred and ideal method of induction. Plus Pitocin or Musoprostol is the preferred and ideal method of induction. It's not clear which one is better than the other, the Pitocin or the Cytotec. I'd say probably locally. My department's preference generally is Cytotec, of course, unless they've had a uterine scar. But either way, you should really be trying to use something else plus this Foley, not just the Foley alone. Okay, well, the fourth tip then is this one might surprise people Don't place the balloon on tension.
Speaker 2:Yeah, surprisingly, this still goes on quite a bit. So historically, these balloons were placed with some weight at the end of it, like a bag of fluid or maybe a half a liter of fluid to place it under some tension, and this causes a lot of pain and discomfort for the patient and also takes away some of her mobility. Today we're doing lots of studies validating the safety of outpatient cervical Foley for induction of labor, and certainly none of those have a weight attached to hanging down. That would make the whole idea impractical. But the truth is we've known for quite a while that connecting these catheters to weight, compared to, just, say, taping it to the leg, is not valuable and just increases the patient's pain and discomfort. I'll put a link to a 2022 review article of this very topic, which concludes that it doesn't affect the time to delivery or the rate of vaginal delivery to place it under traction. They did find in some studies that the balloon came out quicker, but usually you can achieve that goal just by going and checking on the cervix every hour or two. Just pull on it gently and see if it's ready to come out Now. If it's underweight, it'll just slip out at some point and fall out so you may identify it coming out a few minutes earlier than if it's not, but it doesn't lead to a quicker delivery or a lower rate of cesarean delivery and it just hurts quite a bit, to the point that many patients require pain medicine or even epidurals early in still the balloon phase due to what's really an unnecessary intervention.
Speaker 2:I think that there's a narrative fallacy about maybe how these work and this perpetuates this idea. Historically, 100 years ago, we were looking at ways to mechanically dilate and this isn't. It is a mechanical dilator, but that's not necessarily the way it works. We so oversimplify biomolecular processes with physical ideas. We've talked about this with cerclage and cervical insufficiency. This is likely just releasing prostaglandins at the cervix by sweeping the membranes away, pushing them away. It's probably why a bigger balloon works a little bit better, because it sweeps it away and you get a higher dose.
Speaker 2:And, yeah, there may be some mechanical pressure, but the idea that this is a mechanical method is really not validated. That's what led to the Cooke catheter, this double balloon. Let's get one in the cervix and put a lot of pressure on there. It's what led to the idea of putting them under tension. But the fact is, the double balloon and the catheter under tension and all that just doesn't lead to any different outcomes. And yeah, the balloon may come out a little bit quicker, but it probably has a smaller cervix when it comes out. It's just putting it under pressure and making the balloon smaller. I think that when people say this is how it works, that's the start of a narrative fallacy. We don't really know how much of this is mechanical and how much of it is biomolecular, but probably most of it's biomolecular. So you just do the study and if it says that a 50 ml balloon works better than a 30 and that not taping it or not putting it under tension works better, then that's what you do and don't perpetuate narrative fallacies with your learners.
Speaker 3:Obviously, it's not the same action as the baby's head, because this is a balloon of water that is squeezable, whereas the head is a bony structure.
Speaker 3:But we think about doing a DNC, where we're holding the cervix with a tool and then we're putting in progressively bigger and bigger tools to dilate. So it's easy for us to think about the balloon as just like an internal dilator and that's how a lot of us probably even explain it to patients. But from what the clinical evidence shows, probably the idea of even just taping it to the leg and pulling on it is more like the same principle as with placental traction after delivery. It's not the traction itself that is causing the cervix to dilate faster, just like it's not causing the placenta to separate faster. It's just making sure that when it's all ready to come out, then we get it out rather than just letting it sit there. I've heard of cases where a Foley was put in and then suddenly the patient was completely dilated and basically crowning, but the Foley was still in there, presumably like it had probably floated up past or behind the baby's head. I don't know how much the Foley itself was acting anymore.
Speaker 2:Well, if she got to complete dilation. It sounds like it did a great job.
Speaker 3:Yeah, I guess so yeah.
Speaker 2:But generally, yeah, the whole idea of the balloon is that it's against the cervix stretching it out, Otherwise it's just the thin length of the catheter in there, right? I think that that could lead to a bonus tip. Don't insert the Foley too far. In some cases you might unwittingly get behind the placenta that way, which definitely won't help you. Just thread it in just past the cervix, or the balloon portion of it just past the cervix. Feel where the balloon inflates with the first 10 milliliters or so, or you can see it maybe if you have a speculum, and then adjust up or down as needed for the rest of the inflation.
Speaker 3:Yeah, I think if people think about this more as if they're sweeping the membranes, but with a balloon instead of with their fingers, then obviously they wouldn't sweep their membranes all the way up to the the fundus either. Get behind the placenta. Back. When I was initially learning this skill I To avoid inadvertently blowing up the balloon before it was all the way in, I would do the opposite, which was push the balloon as far as I possibly could in to make sure it's really in the uterus, really in the cervix. Then let it get fully inflated and then pull it all the way down, and just a few times. I think I probably did run in to behind the placenta that way, because then I would see some blood coming out of the drain end of the Foley. So that does happen.
Speaker 3:And just in case anyone out there encounters this, you don't panic, it's not an emergency. Even when I've had that happen, it never ended in an acute placental abruption or emergency section or fetal distress or anything. All we would do is pull back on the catheter, pull it back down to the cervix, plug the drain tip so it's not just pulling blood out. You let it clot up and it won't keep bleeding anymore. Fetal tracings would be fine. No tachycystole, no problems. But still you want to avoid having that little scare because it doesn't help you. So just don't even push it in that far.
Speaker 2:Yeah, you also might cause ruptured membranes by pushing it in too far. And I will say if you're using a stylet or or the large tip of the proctoswab to do that and making it more rigid, you're probably going to rupture some membranes if you're.
Speaker 3:If you push it up too high.
Speaker 2:So you do have to think about not pushing straight in if you're using a rigid catheter and angling it so that it slides in and then pull the rigid part back and inflate the balloon. And if you do rupture membranes again, no big deal, put the cap on.
Speaker 3:Yeah.
Speaker 2:It'll. The fluid will mostly stay in there and it's fine.
Speaker 3:Yeah, all right.
Speaker 3:I think this does tend to be one of those things in most cases that a second year OB resident will teach the intern, who then, just a year later, teaches their new interns.
Speaker 3:And there are so many really basic skills and obstetrics that get passed down in this way, and in many cases maybe the teacher hasn't even fully refined their own skillset yet because they're just barely a year into this.
Speaker 3:Other things that get passed down similarly might include an idea of how much oxytocin someone should get in labor or maybe how many pain pills they should be sent home with after a cesarean. But you can see just from this discussion that there is a lot of detail that's easy to get wrong, and I think this applies to a lot of things that seem to be very basic in obstetric training. Some other examples might be how to do cervical checks, how often to do cervical checks, how to break water, how to read a wet mount at the point of care, how to look for ferning the proper way. These are all things that can actually make a really big difference if they're done correctly or not. So we are going to be working on a lot of four tips in the future along these lines that may seem basic but are actually a lot more nuanced than a lot of us think.
Speaker 2:Yeah, these do seem basic, and I bet you, though we'll see from responses, I bet you that a lot of folks are surprised by some of the things we just said about these cervical foleys.
Speaker 2:It's something we take for granted and, frankly, we're not doing it always in an evidence-based way.
Speaker 2:Another thing we might talk about sometime is four tips for dating a pregnancy. A few times a year I see an issue arise with patients who are usually transversive care and they're being treated when I get them for fetal growth restriction, but the truth is they just have an inappropriately assigned due date because their due date wasn't established correctly at the beginning of pregnancy. I was reminded of this the last episode when we were talking about surveilling for fetal growth restriction in twin pregnancies and the difference between small for gestational age and fetal growth restriction small for gestational age and fetal growth restriction. But it's surprising how having a due date that's off just by a few days can significantly impact the percentile that's recorded for the estimated fetal weight. Now, in that case we're talking about using the wrong chart, but in this case, obviously, the wrong due date makes a big difference. It can make a patient appear to have a growth restricted or small for gestational age fetus and then then, of course, lead to overtreatment for potential fetal growth restriction.
Speaker 3:We may have poked the hornet's nest just a little bit with how we used the terms small for gestational age and fetal growth restriction in the last episode, because if you read the ACOG practice bulletin and the SMFM consult series, both regarding growth restriction, they very clearly state that growth restriction is defined as estimated fetal weight under the 10th percentile or abdominal circumference alone under the 10th percentile.
Speaker 2:Well, I love poking hornet's nest, our job is to encourage thought and if we've, if we make you think about something in a way you haven't thought before or show maybe a deficiency in understanding, and encourage some thought and conversation, then we're doing a good job. So we know how the words are currently defined and used, but the point of all that was that we are over-pathologizing many cases by using the term fetal growth restriction too broadly for fetuses that don't actually have growth restriction.
Speaker 3:And they also use the term small for gestational age in a way that they suggest only applies to newborns that have been weighed on a scale, not to pregnancies that have been measured by ultrasound.
Speaker 2:Right, yeah, I know, and we talked about that offline and a little bit online.
Speaker 3:Yeah.
Speaker 2:We definitely know what the terms mean, and if you read pick up your recent edition of Gabby's Obstetrics, it'll disagree with that a little bit. So don't be so narrow-minded about how these terms are applied. These things change over time. Now, I would love for anyone, though, who thinks that the comments were beyond the pill a little bit in terms of how we use those terms and how we're going to use them today. Frankly, then they should read the new Royal College of OBGYN's Green Top Guideline, number 31, just published last month in the British Journal of Obstetrics and Gynecology.
Speaker 3:How exciting. What's this one called.
Speaker 2:Well Small for Gestational Age Fetus and a Growth Restricted Fetus. Investigation and Care.
Speaker 3:How nice. I really do truly love these British Green Top Guidelines. They're just such a treat. And I know you're already going to do this, but why don't you go ahead and read the first couple paragraphs?
Speaker 2:Thank you, I will, although the title really does give it away right. I will, although the title really does give it away right. I mean for the people whose ears were burning in the last episode when we said small for gestational age fetus. That's the name of the bulletin, but the first two paragraphs really capture this in a way that maybe we didn't do a good job of, or I didn't do a good job of last episode. So I'm just going to read this from this month's British Journal.
Speaker 2:A fetus is considered SGA when individual biometric measurements or a combination of measurements used to estimate fetal weight fall below set parameters and require accurate assessment of gestational age. Commonly, the definition of SGA refers to a fetus with a predicted weight or an abdominal circumference measurement less than the 10th percentile. Sga at birth is commonly diagnosed based on a birth weight below the 10th centile. They actually say centile, he's British and often birth weight charts are adjusted for the sex of the baby.
Speaker 2:Fetal growth restriction FGR implies a pathologic restriction of the genetic growth potential. Some, but not all, growth-restricted fetuses infants are SGA. The likelihood of FGR is higher in fetuses that are smaller. Growth-restricted fetuses may manifest evidence of fetal compromise abnormal Doppler studies, reduced liquor volume, the amniotic fluid, for all you Americans. Defining FGR and thus diagnosing it in a current pregnancy is challenging because of the need to determine growth potential. Similarly, risk assessing whether FGR existed in a previous pregnancy presents a different challenge. There is a need to focus on those fetuses at risk of adverse outcome, and thus those who are FGR rather than SGA, using varying parameters such as sequential ultrasound measurements, doppler assessments and biomarkers.
Speaker 3:So previously we had a lot of criticisms about the green top guideline about thromboprophylaxis in pregnancy, but this one is just gold. It's perfect and although it was just published last month, for us right now in 2024, it was put online in May and it does show the power of language and how the words that we use affect our thought processes and understanding of what's going on sort of power of words again at the end of this episode.
Speaker 2:But we should consider adopting this language of the Royal College and I don't know how to talk about these topics like we did last episode and like we're going to discuss a little bit more today. I don't know how to talk about them without using the language that they've defined there to help guide this conversation. So if someone's being overly pedantic about how these terms are used in some of our American literature not even all of it and only for the last few years right then I think that they're missing the point entirely that those two paragraphs really make. We need to be precise with our language when we can be and we don't need to be limited by pedantic definitions of it. And we can say a small for gestational age fetus, and we can say a small for gestational age fetus. And we can say a small for gestational age newborn. And we can say fetal growth restriction when we believe that's what's going on, or failure to thrive for the newborn population, and that precision and clarity is important in caring for our patients.
Speaker 3:Okay, did you wanna just get to how to date a pregnancy now and not wait till later?
Speaker 2:Well, sure, there's a lot.
Speaker 2:There's a lot to that, but I but there is a there's a point about this related to growth restriction that I want to make.
Speaker 2:So this is usually something that you, of course, you want to do at the first visit if possible, and I think everyone listening assumes that they know how to do it, and if they're practicing OBGYN, this should be bread and butter, but clearly that's not always the case by how many patients I see who have misdated pregnancies.
Speaker 2:Now there is a 2017 ACOG committee opinion it's number 700, that talks about methods for estimating the due date. It recommends that an estimated date of delivery be assigned as early as possible, and ideally with the help of a first trimester ultrasound. That's correlated with the dating based on the last menstrual period. Now women don't always remember the first day of their last menstrual period correctly, and they report that perhaps 40% of patients will have a discrepancy in the dates between based on their last period versus a first trimester ultrasound. So first trimester ultrasound, of course, is better than a second trimester ultrasound because of the margin of error of ultrasound, and so only about 10% of women in the second trimester will have their due dates changed as the accuracy of ultrasound becomes greater.
Speaker 3:Yeah, so that says a lot If 40% of people would have their due date changed if they had a first trimester ultrasound, but then out of that same population only 10% would change because, like you said, the margin of error is greater. So that shows that we're more likely to go with an erroneous estimate based on an inaccurate LMP if we don't do a first trimester ultrasound. But they also mentioned in this committee opinion that, in addition to not remembering the first day of the last menstrual period, this method of adding 280 days which is what all of the calculators do to the first day of the LMP which is, I think, the way I would remember it is add a year, subtract three months, add seven days.
Speaker 2:Nagel's rule.
Speaker 3:Yeah, that method does not account for variation in the menstrual length or variation in the timing of ovulation. Specifically and I think that's the big point that you're wanting to make here- Exactly.
Speaker 2:So we all know what the Bolton says. We've summarized it very quickly. So we all know what the bulletin says. We've summarized it very quickly For the earliest ultrasounds you should change the due date If the ultrasound performed before nine weeks is more than five days different. That's what the bulletin says. That gestational age that you should go with what the ultrasound says even though it's less than five days different. But overall, acog has made this really simple and clear cut and people usually are following the criteria as listed in the committee opinion. But that's not where the error is coming in, that's not where folks are getting this wrong.
Speaker 3:Yeah, I do agree with that coming in. That's not where folks are getting this wrong. Yeah, I do agree with that. That there is still enough margin of error when you get really early.
Speaker 3:I used to do my own dating ultrasounds. I don't anymore, but I remember in some of these early cases when it's like the first day you could possibly see a heartbeat, and especially I wouldn't have really ultra precise ultrasound machines. They'd be really old, probably from the nins. I'd zoom in all the way on the baby and it would look fuzzy on the screen. We could see the pulse.
Speaker 3:But to have to try to distinguish the crown and the rump even a half millimeter off can greatly affect the estimated dating, and so a lot of times in those cases I'd give a provisional measurement and say we should measure this again in a few weeks and probably go by that one instead. But another issue I see is people think it is standard to assume, no matter what kind of cycle length they actually have, take their LMP and just plug it in as if it's a 28-day cycle, even if the patient has been tracking it well, even if they have a known date of conception or very regularly are not 28 days and they know this. In general, we actually do need to correct the LMP date for the length of their menstrual cycle and not assume everyone has a 28 day cycle.
Speaker 2:Yes, and then in the right set of circumstances, that can significantly magnify that error of not adjusting for the cycle length, can significantly magnify the error in the due date and lead you to assign the wrong due date by as much as a week or even more, even though it seems like the ultrasound was consistent with or congruent with the dating by the last menstrual period.
Speaker 3:Okay, why don't you walk us through this a bit more?
Speaker 2:Well, we've all been taught that a normal menstrual cycle is anywhere between 21 and 35 days, as long as the patient is ovulatory, and for most of those women, the luteal phase is relatively fixed, so the follicular phase will be variable. Now there's actually some variation in the luteal phase as well, but 95% of patients have a luteal phase of between 13 and 15 days and almost all of them have a 14 day luteal phase. So if you have a textbook average 28 day cycle, then you'll ovulate on cycle day 14. And that's the assumption that's built into this idea that when we date a pregnancy by adding 280 days to the first day of the last menstrual period to determine the due date. But if you have a 35 day cycle, you probably ovulate on day 21, because it's 35 minus 14. And if you have a 21 day cycle, you probably ovulate on day seven. So you have to adjust the due date that's given to you by your calculator or your wheel or your app or whatever, by adding or subtracting to the due date the variation in the cycle length.
Speaker 3:So you're supposed to ask what's the first day of your last menstrual period? And then the next question should be what's the average length between your cycles? And if someone has a due date, let's say March 15th, based on the calculator, from what they told you their LMP was, that's going to assume a 28-day cycle. But then she tells you I have 34-day cycles, then you need to add six days to the estimate to account for the fact that her ovulation likely was six days later than that typical 28-day cycle would have estimated.
Speaker 2:Yeah, that's it, and I think almost no one does. This is the problem. So there's a relatively new paper published in the last year that analyzes the average menstrual cycle length in a large number of women, and this data comes from the Apple Research Group because it's based upon the Apple Health app. So we're seeing a lot of this Apple Health app data being published in different formats and this coming from all this accumulated digital devices and this is a really good basic information for us. It included over 125,000 menstrual cycles from about 17,000 participants and they found, of course, that the median menstrual cycle surprise was 28 days, with an interquartile range of 26 to 30 days. So that would mean that the middle 50% of patients had periods that were somewhere between 26 and 30 days.
Speaker 2:Now they were studying in this paper a seasonal variation that occurs, with menstrual cycle links and also the changes in cycle lengths that were dependent upon where you lived in relationship to the equator, and there's definitely some interesting things there. But the only point I want to make from this paper for our present purposes is that 50% of women the outlying 25th and 75th percentile groups there they have cycles less than 26 days or greater than 30 days in length, so the majority of patients will have their due date adjusted by anywhere from one to seven days plus or minus. If people simply ask the question about how long their average menstrual cycle length is, this is honestly easier than ever to know because so many of our patients are tracking their cycles on, like the Flow app or the Apple app or other apps like this.
Speaker 3:Okay, so you have an example of how not accounting for this can lead to significant mistakes and even potential harm. I know you wrote a Howardism post several years ago that gave a similar example and in that case, as I recall, the patient was actually induced early due to suspected fetal growth restriction at 37 weeks, even though if the correct due date had been used by correcting for her cycle length, she would have had no reason for an early induction.
Speaker 2:Yeah, exactly, and we can put a link to that.
Speaker 2:But I actually see this several times a year, so I'll change the numbers around a bit for this real patient.
Speaker 2:But give an example with real numbers, real data at least, of a recent patient I saw and we can use for this example the due date, the pretend due date you just had, of March 15th, and of course that's based on adding 280 days to the an ultrasound due date of March 19th, where the LNP the 280 days plus LNP due date, would be March 15th. So since this is less than five days difference, then her due date would remain March 15th, according to our normal practice. Now, by the time she has her anatomy ultrasound a few weeks later, a few months later, the estimated fetal weight using the March 15th due date places the fetus in the ninth percentile. So this patient then is sent to maternal fetal medicine for further evaluation and over the next six weeks or so she receives two additional growth ultrasounds along with a variety of Doppler studies and other things that one might do while investigating growth restriction, and these place her again in the 10th and 8th percentiles respectively.
Speaker 2:Now the growth restriction that they observed was symmetric, although I realize we don't really talk about symmetric and asymmetric growth restriction anymore, or we don't distinguish those and use those terms.
Speaker 2:So just anticipating the responses, that I'm using out-of-date terms again, but they're useful when you're thinking about the differential diagnosis. So we stopped using these terms because sometimes they lead to premature closure of the diagnosis. For example, if it's a symmetric growth restriction, you may assume that's not due to placental insufficiency and is due instead to a genetic or chromosomal problem. Or if it's asymmetric, you might assume it's not due to the other, and so we sometimes are just making the wrong diagnosis because there's a lot of overlap in the causes of symmetric and asymmetric growth restriction. But for the most part, you can still assume that if you're seeing symmetric growth restriction in the mid-trimester and it's not due to some apparent genetic or chromosomal abnormality, it's probably not due to placental insufficiency, unless the patient has antiphospholipid antibody syndrome or something like that. This idea of early uteroplacental insufficiency is probably due to a misassigned due date, and so it is helpful to know that this patient had what was labeled as symmetric growth restriction, with no risk factors and no apparent genetic or chromosomal abnormalities.
Speaker 3:So did she have any risk factors for any of those issues, maybe hypertension, diabetes or anaphospholipid antibody syndrome? Was she a smoker?
Speaker 2:Yeah, no risk factors at all, nothing. Perfectly healthy, normal body weight, nothing at all. And by the time I saw her, the warning bells had been rung and plans were afoot for intensive monitoring and testing, with all the antenatal surveillance and all the things you can imagine, and probably early delivery, et cetera.
Speaker 3:And that would include things like umbilical artery dopplers, which of course, shouldn't be done in fetuses that don't have growth restriction, because the false positive rate is so high that it can lead to unnecessary intervention and, in some cases, even extreme iatrogenic prematurity.
Speaker 2:Yeah, not to mention all the other tests that have potential to generate just the BPPs and NSTs that have the potential to generate false positives that lead to unnecessary early delivery. So you're applying a bunch of sort of low quality tests to a patient who's not at risk for the conditions you're testing for, and that means that any positives you might get, like low fluid or abnormal Doppler velocimetries or things like that these are likely going to be false positives.
Speaker 3:Well, we do know that these can truly happen in people that are at low risk, and so just the absence of risk factors doesn't mean just throw it all away. But that starts with having an accurate due date. Yeah, what happened in this case? This patient who had the inaccurate due date, and all of this.
Speaker 2:Right.
Speaker 2:So since I realized that one of the most common reasons for suspected fetal growth restriction is an inappropriately assigned due date, and because I see this quite commonly, then my first question to her very first question was what's the length of your menstrual cycle?
Speaker 2:And in fact she had been tracking them and they were 33 days.
Speaker 2:So, if you recall, this LNP due date was March 15th, our pretend due date based on a assumed 28 day cycle, but then it would be March 20th if we adjusted the LNP assigned due date and corrected it for her 33 day cycle length.
Speaker 2:Now the ultrasound due date said March 18th, which is within the margin of error of both due dates, either March 15th or March 20th, if you wouldn't change based on either one. And so it becomes very important then that you actually have the right due date based upon the LNP in this situation. Now, when I went back and adjusted her sonographic findings and each of the ultrasounds to the corrected gestational age based upon the correct due date, then it turns out that she was around 35th percentile at the time of these ultrasounds and both parents, by the way, they're under five foot six, and so a 35th percentile fetus for a mom and dad under five foot six makes a lot of sense. It's what you would expect and in actuality there's just no evidence at all that there was a either small for gestational age fetus, using the British definition of the term, or especially growth restriction fetal growth restriction, using any definition.
Speaker 3:Yeah, you can imagine that if this pregnancy had measured anything smaller, let's say 15th percentile with her accurate dates, then a difference of even two or three days could have easily shifted this from a normal pregnancy into even severe growth restriction category.
Speaker 2:Yeah, absolutely. In fact you can do these, you can play around with this. If you go over to perinatologycom and you put in a 24 week and two day pregnancy that weighs 605 grams, you'll see it's a 15th percentile pregnancy. Now if you just change that to 24 weeks and four days so that's just two days different, two days different of an assigned LNP, that now becomes a ninth percentile pregnancy. So just two days difference can move a normal pregnancy into a zone of concern. And then all of these unreliable tests will follow and you may see a patient harmed by false positive results.
Speaker 3:Okay, so the takeaway is most women need their due dates adjusted based on the average length of their menstrual cycles.
Speaker 2:Exactly.
Speaker 3:Okay, I have one more little pet peeve about this dating stuff. So I was taught that when you're reporting the due date you have to say what they were measuring at the dating ultrasound. For example, let's say a patient presents and by her last menstrual period she's 10 weeks. She gets an ultrasound. The ultrasound measures her at nine plus five weeks and let's say this is with an accurate period, We've made the correction, et cetera. How would you report that dating criteria?
Speaker 2:Well, I think to convey all the information, I'd say she's 10 weeks based on her LMP, consistent with a nine week five day ultrasound.
Speaker 3:Yes, exactly. But sadly I see most people already skipping that step in their heads and just reporting the due date and the gestational age that they had finally assigned. So in other words, I would often see this kind of thing reported as 10 weeks by LMP and 10 week ultrasound, because they had decided that day that, yes, your ultrasound is consistent with you being 10 days, and so they just say it's a 10 week ultrasound, but she was measuring nine plus five. So that's my pet peeve that people don't use the actual dates and the actual measurements when they're reporting the full criteria, because doing that helps other people not have to do a big deep dive later on if there ever becomes any question in the future about the due date.
Speaker 2:Well, I don't think that's too nitpicky. The point is to know how discrepant they were and understand where error might have occurred. And in the patient we just talked about had been reported in the wrong way. You wouldn't have even known that there was a discrepancy between the two that might have favored, in fact, a fetus that wasn't as far along, and then you might not have thought to ask the question. Wait a minute. Could we have messed up the LNP dating or things like that?
Speaker 3:Well, you owe us a story now.
Speaker 2:A story, a telenovela.
Speaker 3:Yes, a history tidbit.
Speaker 2:Well, how about a little history about postpartum depression?
Speaker 3:All right. Well, that's a big topic, but let's go ahead.
Speaker 2:Well, okay, A few points about postpartum depression that are of historic and perhaps literary interest. So we didn't use the term postpartum depression really until about the mid-1990s. Before that you see a lot of the term postnatal depression.
Speaker 3:We're always renaming things, aren't we?
Speaker 2:Yeah, we are. That's the theme of some of what we've been talking about. Is we rename them and then people think that they know something. Other people didn't because we use a different term. But yes, it's undoubtedly the same thing but renamed a few times. And in 1994, this happened the DSM-IV was published and that recognized major depressive disorder with postpartum onset. So the term postpartum depression came into vogue. But obviously women have had postpartum depression before 1994. And actually the term postnatal depression itself was relatively rarely used prior to the 1970s. So I guess every 20 or 30 years we have to rename something. A paper from 1990 that I found showed that only about 24% of women who likely had postpartum depression, based upon the symptoms reported in their chart at least, had been identified as having postpartum depression by their physician. So most of the diagnoses were going missed.
Speaker 3:Well, they likely weren't screening for it. Screening today still probably remains an issue, but I think we're doing a lot better job of it now than we were in 1990.
Speaker 2:Yeah, I'm sure, and either not screening or just glossing over it as postpartum blues or some minor ailment, you're just tired, you're just adjusting. A lot of older research focused on marital status, even from the 70s and stuff where the problem was just you're unmarried, and so I guess the solution was to get a husband.
Speaker 3:No, no comment.
Speaker 2:Well, but it's an example of where it might appear on a superficial level that postpartum mood disorders are on the rise if you just looked in the incidence rates and track the numbers of people who've received the diagnosis. But the truth is we've had an expanded awareness, we've used new and more encompassing terms and we've created screening programs that all have the effect of making the diagnosis appear more prevalent.
Speaker 3:But it has been around forever as long as there've been babies born.
Speaker 2:Forever. So Hippocrates was aware of the condition and actually believed that it had an organic cause, and the first modern serious author was a Dr, marseille in 1858, who described a special change in mood that seemed to be unique to him in the postpartum period. But in the 19th century a unique postpartum condition, for the most part, was relatively unknown and it wasn't part of the popular culture or conversation about pregnancy. But it definitely existed, and so you have to look beyond the terms and the words and even the diagnostic criteria to see it, and it's amazing how having a name for something affects our ability to see it or understand it.
Speaker 2:I think that's my point about fetal growth restriction versus small for gestational age. When you realize that pregnancies under the 10th percentile may just be small for gestational age and not actually growth restricted, you start to think about these things differently. And the same thing for depression and a lot of other things. Autism we discussed last episode too, in the same problem. Well, in 1798, wordsworth wrote a poem called the Mad Mother, which described a woman who, along with her newborn, was abandoned by her husband and then experienced a mood disorder.
Speaker 3:So, according to Wordsworth at least, the problem is a lack of a husband.
Speaker 2:Well, you're seeing a cultural narrative there, obviously, but yeah, I don't think Wordsworth was a psychiatrist. But it is typical of how mental health problems among women were viewed and, frankly, the move to attributing mood disorders to organic causes over the next hundred years didn't help much.
Speaker 3:Yeah, because we get the ideas of hysteria got to remove the uterus and that'll cure everything, or the concept that hormones were the cause.
Speaker 2:Right which is still pervasive today, even though hormones are not the root cause of mood disorders in women.
Speaker 3:Yeah, thanks a lot, freud yeah.
Speaker 2:Sometimes a cigar is just a cigar. Well, postpartum psychosis is what really raises to the level of social consciousness in the 19th century, the more extreme cases of mood disorders, not just what we might call postpartum depression today. It was the extreme cases of what we might call postpartum depression today. It was the extreme cases of what we might call postpartum psychosis today, but it didn't have a name and it really wasn't described in much of the literature of the time. So that's what, when you think about postpartum depression in the 19th century? Today we'd probably call it postpartum psychosis. Have you read the Awakening by Kate Chopin Chopin?
Speaker 3:I really. I have got two little boys so I really have barely time to read anything, even a text message. So have you read it?
Speaker 2:I have. I read it in high school. It was assigned reading. Well, I'll tell you about it.
Speaker 2:So the central character is a woman named Edna and the book is about she undergoes an awakening through a period of liberation and self-discovery. So the book explores her feelings of being trapped by societal roles, as a wife and a mother. She has an affair with a guy. He ends up leaving her. And then the final scene of the book, the last few pages. She walks into the Gulf of Mexico and drowns herself. Although when you read this as a younger reader it's not like clear what happened, Like it's, it leaves some room for interpretation, but she dies by suicide.
Speaker 2:Anyway, the ideas of depression, and certainly postpartum depression, weren't really understood when the book was written in 1899. But she describes her feelings of isolation, aimlessness and despair and many readers gloss over the impact of her children and the description of detachment from them that today we might call postpartum psychosis. Now, earlier in the book there's a scene where Edna attends the birth of a friend of hers, a Madame Ratineau, and she's reminded of her own birth experience and she talks about that. She recalls her own birth where they had been dulled by the use of chloroform, and this seems to be a metaphor of her feelings of detachment for her children.
Speaker 2:Chopin writes Edna began to feel uneasy. She was seized with a vague dread. Her own life experiences seemed far away, unreal and only half remembered. She recalled faintly an ecstasy of pain, this heavy odor of chloroform, a stupor which had. And at the end, as Edna, as she walks into the water, near the very last few pages of the book Chopin again writes, few pages of the book Chopin again writes, she thought of Leonce and the children. They were a part of her life, but they need not have thought that they could possess her body and soul.
Speaker 3:So Leonce was the boyfriend, a fair person, right?
Speaker 2:But this sounds like detachment that we see with maternal postpartum psychosis, in the worst cases, maternal suicide.
Speaker 3:Was she very recently postpartum in this book.
Speaker 2:No, and not in the book, but Kate Chopin, the author, might have been, and so she's likely writing about her own experiences. So Chopin herself in real life never heard of the ideas of postpartum depression or psychosis.
Speaker 3:Yeah, because those words didn't exist Right.
Speaker 2:But she did have six children and shortly after the birth of her last child her husband and then her mother in short order died. She was all of a sudden economically ruined and had a comfortable life up to that point. She apparently had a brief affair with a man who was helping her at that time of her life with finances and her children, but then she was shamed for this and she moved away. And then her mother died. And all this happened to her in very short order after the birth of her last child.
Speaker 3:So there's a lot of highlights from the book, minus the part of drowning herself right.
Speaker 2:Yeah, it's semi-autobiographical. I think most of us accept the fact that this is semi-autobiographical about her own life, and so all these events in the book are compressed in real life. For her, they're compressed into a period that was all within a year or two of the birth of her last child and in fact she was being treated by her obstetrician for depression or melancholia they would have called it then and the obstetrician recommended to her that, as a form of therapy, she take up writing.
Speaker 3:So that's how she wrote the Awakening, as a therapy for herself.
Speaker 2:Well, originally she started with some short stories and then she found she could make money. So you think about how can a woman with six children support herself by working at home, essentially. So she wrote some short stories and poems and sold them to magazines. But she began writing, yes, what would become her magnum opus, the Awakening. And the feelings that Edna feel in these scenes undoubtedly describe how Chopin herself must have felt in that time period, in that year or so. The problem she was dealing with after the birth of her last child, so you have to wonder was she suicidal herself?
Speaker 3:But she didn't actually die by suicide, did she?
Speaker 2:Well, obviously no. Her obstetrician supported her and gave her a venue of therapy, but undoubtedly, I feel like she's describing the thoughts and feelings that she had, and probably was suicidal, for a long time.
Speaker 3:Well, I don't know that. I've told my patients you should start writing, but I do wish in general that we had a lot more kind of well-rounded, different options that we could offer patients once we've screened and identified them.
Speaker 2:And we certainly have a lot more available today. Think about what therapies were available to her then.
Speaker 2:Journaling and therapy may be a form of therapy, but today we have good medicines and we have inpatient therapy if needed and we have lots of options to hopefully prevent people from getting that sick. Well, I'll also mention in the context of this the poet Sylvia Plath, who I know. You know, plath had a long history of depression. She attempted suicide in in 1960. And then a second child, nicholas, was born in 1962. Now, in between those pregnancies she had a miscarriage in 1961. And apparently this miscarriage happened after Ted had beat her, or so apparently she told a therapist.
Speaker 3:Okay, well yikes. Obviously, a history of mental health problems, especially with a prior suicide attempt, predisposes patients to worse postpartum mood disorders as well. And then if you throw in intimate partner violence and the loss of a baby, you have this complete storm of trauma. Yeah, I don't know, what else could have made that possibly much worse than what she already had going on?
Speaker 2:Yeah, and the same kind of series of events we see a lot of times in patients. You don't have to have all these external factors, but obviously in Kate Chopin's life she had personal tragedies and external events happen at the same time in that period which made these worse. And here we see this with Sylvia, where she has a history of mental health problems, predisposed to some anticipated problems, and so she wrote a number of poems, famously now, about this perinatal loss, and the most prominent of these was called Parliament Filled Hills, which she wrote just a week after the miscarriage and then added to all that around 1962, I think while she was pregnant with the second child, she found out that Hughes had been having an affair while she was pregnant.
Speaker 3:So it does get worse. Well, unfortunately that does seem to be a peak time for infidelity, during pregnancy and the postpartum period.
Speaker 2:Yeah, and she had a car accident around this time. That was actually, as it turns out, a suicide attempt. And then, finally, in 1963, at the age of 30, she died by suicide. She wrote probably her most profound volume of poetry, ariel, in the months before her eventual suicide.
Speaker 3:So at that time she left behind a three-year-old and one-year-old baby.
Speaker 2:Yeah, so she died of postpartum depression.
Speaker 3:And this was despite not only writing but actively receiving what treatment was available at the time, Although I'm sure the unique nature of postpartum depression and how that affects mental already underlying mental health issues, I'm sure it wasn't very well understood back then.
Speaker 2:And I think we still don't understand all this very well.
Speaker 3:Yeah, you're probably right, but I think there's been ongoing efforts. I think this is something we're continuing to try to improve. I don't know, but hopefully, if Sylvia Plath had lived in this generation, maybe things would have been different for her and her kids. Maybe not, but I'm sure she would have at least gotten some different treatments. So maybe she would have been different for her and her kids. Maybe not, but I'm sure she would have at least gotten some different treatments, so maybe she would have had a better outcome. The Thinking About OBGYN website will have links to what we've talked about today. Our Instagram page is always getting updated, thanks to our ninja Maddie White, and check us out again in a couple weeks.
Speaker 1:Thanks for listening. Find us online at thinkingaboutobgyncom. Be sure to subscribe. Look for new episodes every two weeks.