Ep 22: All About Your Due Date

Speaker 1: Today, I'm clearing up all the confusion about your due date.

Speaker 2: Welcome to the All About Pregnancy and Birth podcast. I'm your host, Dr. Nicole Calloway Rankins, a board certified Ob Gyn physician, certified integrative health coach and creator of The Birth Preparation Course, an online childbirth education class that will leave you feeling knowledgeable, prepared, confident, and empowered going into your birth. Quick note, this podcast is for educational purposes only and it's not a substitue for medical advice. See the full disclaimer at www.ncrcoaching.com/disclaimer.

Speaker 1: Hello, welcome to another episode of the podcast. I am glad you're here with me today as I am talking about your due date. Your due date is really important. All of the decisions that happen during pregnancy revolve around your due date, so it's really crucial that we get it right. So in today's episode I'm going to talk a little bit more about why it's important. I'll tell you the best way to determine your due date. And I'll also talk about why it's important to understand that your due date is an estimate. Now before we get into the episode, let me give a quick shout out. This is to Danielle DB. She wrote in a review in iTunes, I discovered Dr. Rankin's podcast when she was a guest on the Evidence Based Birth Podcast and have been hooked, since the topics are clear and super informative and the information is easy to digest, it is refreshing to hear an Ob speak about lots of topics that are super important to pregnant women from a place of compassion, respect and patience. This is a fantastic resource for anyone looking to understand more about the pregnancy and birthing process.

: Well, thank you so much for that lovely review Danielle, and I think this is the same Danielle who I know from the podcast community Facebook group too, so I really appreciate those kind words. I love to give shout outs on the podcast, so if you have something you'd like to share about the podcast, please leave it iTunes review so I can give you a shout out in a future episode.

: All right, so let's talk about your due date. So your due date is more than just about giving you an idea of when your baby's going to be born. An accurate due date is absolutely critical during your pregnancy. Really all of our management decisions during pregnancy are influenced by your due date because we make our decisions based on how developed your baby is and how far along you are in your pregnancy, your gestational age. And your gestational age, how many weeks you are in pregnancy, is determined by the due date. And again, we make all of our decisions around this, whether or not you are considered preterm, whether or not you're post-term, past your due date. Certain tests such as testing for gestational diabetes need to be done at a certain time. Genetic testing to look for any genetic abnormalities needs to be done at a specific time in pregnancy. Having an accurate due date will reduce your labor being induced. So it's really, really important that we have an accurate due date in pregnancy. I can't stress that enough. It's like one of the fundamental most important things about pregnancy.

: Now, the first thing I want to say about due dates besides the fact that it's really important is that your due date is an estimate, it is not an exact prediction of when you would go into labor. Actually only about 4% of women will deliver on their due date. Now part of that is because of the limitations of the methods that we use to estimate due dates, and I'll talk about those methods in just a minute, but also part of it is just the natural biologic variation in the way babies develop. Some babies are ready a little bit sooner, some babies take a little bit longer to develop. I actually wish that we would stop giving a due date and instead we would give like a range of dates that we expect that you'll deliver, like in the range of probably I would say five to seven days will be a reasonable thing to give because it's easy to get fixated on that date and when you go past that day you get concerned. I really think that it would be much better if we just gave an estimate for when you may be due as opposed to the due dates of don't get fixated on that specific date in terms of it being an accurate prediction of when you'll go into labor, because like I said, only 4% of women deliver on their due date.

Speaker 1: Now, as a matter of fact, going past your due date is very, very common, especially if it's your first baby. It's so common that I included it as a bonus lesson in my online childbirth education class, The Birth Preparation Course. I'm not in the office anymore. I don't do prenatal care. I only work in the hospital as a hospitalist, but when I was in the office, I would recommend induction no earlier than 41 weeks. As long as everything was going okay at 41 weeks, the risk of stillbirth starts to go up. So either induction or closer monitoring, but again, I have a whole bonus lesson along with some other great and fantastic stuff in my online childbirth education class, The Birth Preparation Course. You can always check that out on my website in www.ncrcoaching.com/nirth-course.

: All right. As far as how we estimate the due date, the traditional way of estimating the due date has been to add 280 days from the first day of your last menstrual period or if you know the exact day of conception, then add 266 days to that. However, this method is flawed because it assumes that all women have regular menstrual cycles that are 28 days and that ovulation occurs on the 14th day and that couldn't be further from the truth. Your cycle varies quite a bit and not everyone has a 28 day cycle. Some women have shorter, some women have longer. You don't always ovulate on the 14th day of your cycle, so that method has those flaws because of that. That method also doesn't take into account that a lot of women just really don't accurately remember the first day of their last period. It's very often a guess unless you keep track of it using something like an app. I know if I didn't use an App to keep track of when my last menstrual period was, I would have no idea, would just be roughly a guess. I think it was a couple of weeks ago. It was three weeks ago. I just don't keep that close track of it so that method has those flaws for that reason.

: The best way to estimate due date is ultrasound and ideally an ultrasound before 22 weeks of pregnancy. Now actually a crown rump length and that's exactly what it sounds like. It's the distance from the crown, the top of the baby's head to the ramp, the baby's bottom, a crown rump length measured on ultrasound in the first trimester up to 14 weeks if that's available. That is the most accurate method of determining due date. It's more accurate than any other ultrasound done at any other point during the pregnancy. So if you can get that early ultrasound and measure that crown rump length and it varies with different doctors, a lot of doctors routinely we'll do an early ultrasound to date pregnancy or you're getting an early ultrasound because of being offered or wanting to do genetic testing.

Speaker 1: So a lot of people will have that early ultrasound. And again, that's the most accurate way to determine due date. Now once we get an ultrasound estimation of your due day, we can pair that with the due date that we got from your last menstrual period and come up with a final estimate of the due date. Now if those things are within about seven to ten days of each other, depending on when the ultrasound was done, but roughly seven days, if your last menstrual period and the ultrasound date are within seven days of each other, then we'll go with your last menstrual period. So for example, if your last menstrual was May 1st and the ultrasound estimate of your due date is May 5th then we'll go with a due date of May 1st based on your last menstrual period. But if it's a difference of more than seven days, so if your menstrual period says May 1st and the ultrasound says May 11th then we're going to go with the ultrasound date of May 11th because that's more than seven days in the ultrasound.

Speaker 1: In that case, it's going to be more accurate. So then your due date, your final due date from that earliest ultrasound, will become your estimated due date. And here's the thing that I see a lot of women get confused by. Your due date does not change. It stays the same. Even if you have another ultrasound later in pregnancy, we always go by that due date from that earliest ultrasound measurement. That's your final due date. Now, every time you have an ultrasound in pregnancy, they're going to put the numbers in and the measurements, and they're going to come up with an estimate for a due date. But your due date does not change. Your due date will always be whatever it was based on that earliest ultrasound. It doesn't change. I see that a lot of women get confused by that.

: Now we used to use old school wheels. They're like physical wheels in order to estimate how far along you are in pregnancy. Once we had your due date, studies have shown that those are actually pretty inaccurate. There are calculators that do a better job of determining how far along you are in pregnancy. There are a lot of apps and whatnot. They can do that. You do have to be careful because there's studies that have also shown that those apps are not accurate either, so just be aware of that when you download that stuff and compare it to what your doctor is using. Most doctors' offices use verified programs within an electronic medical record that'll tell you how far along you are in your pregnancy based on new due date. So you can always bring in whatever app you have on your phone and compare it to make sure they match up.

Speaker 1: Now if no ultrasound is done before 22 weeks, then a pregnancy is considered sub optimally dated. Okay. That means that we don't have a really good estimate of what your due date is. If we don't have an ultrasound before 22 weeks, if we have one before, then have a pretty good estimate after that. Not so good. And in that case, if the first ultrasound that you had is after 22 weeks, then it's not appropriate to rely on just that single ultrasound to decide how far along the pregnancy is. And as a result, what the due date is. Because an ultrasound that late can be off, it can be off quite a bit. Ultrasound into the third trimester can be up at up to three weeks.

: So a single ultrasound done later in pregnancy is not reliable. If the due date doesn't match with your last menstrual period, it could be that the baby is smaller than expected. It could be that you're further along than you thought. It's just not reliable or accurate. So what we do, if you haven't had your first ultrasound before 22 weeks, then we repeat the ultrasound in three weeks. And it shouldn't be any sooner than three weeks. Because if you do it sooner than that, the measurements can be unreliable. So really you need to repeat it in three weeks, three to four weeks and compare the growth between those two ultrasounds. If normal growth has occurred, then we can more confidently say that we know what the due date is, so based on the growth from one late ultrasound to one later ultrasound. If things look good, then we can confidently say, okay, here's our estimate of the due date. However, if the growth has not occurred, then it's possible that the baby is smaller than we expect even though you're further along in pregnancy or if the baby is growing bigger than we expect the maybe the baby is bigger than we thought based on how far like a far along you are in pregnancy.

Speaker 1: I feel like that sounded really confusing, but the short story is that you have to do a couple of ultrasounds, three weeks apart. Compare those and then come up with your best estimate of how far along a pregnancy is. Whether you're right on target, whether you're behind with the due date or ahead with the due date. And again, that's only if that first ultrasound was done at 22 weeks or later. If that first ultrasound was done at 22 weeks or later than one exam is not reliable and we need to repeat it in three or four weeks to get an accurate assessment of the due date. Now if you conceived by assisted reproduction, so if you conceived by invitro fertilization or intrauterine insemination in, you know, the exact conception or fertilization date, then you can definitely reliable tell when the due date is. And there are calculators or apps that can calculate the due date and how far along you are based on the conception or fertilization date, not the last menstrual period, the fertilization date.

Speaker 1: You can even put in like the date that you isolated the date of the egg retrieval, the date of insemination. So there are lots of options available to specifically, really specifically date a pregnancy. If it was conceived by assisted reproduction.

: All right, so that's it for your due date. It's not a whole lot, but just to summarize again, your due date is important. All of the decisions that we make during pregnancy are based on your due date, how far along you are, whether or not you're preterm or if you're post-term, what tests you get. So it's really, really important to have an accurate due date. You're due day is best determined by an ultrasound in the first trimester, that crown rump length, but as long as it's done up until 22 weeks of pregnancy, it's very reliable in terms of estimating and accurate due date.

Speaker 1: Once your due date has been established, it does not change based on future ultrasounds. So your due date will always be what is determined by that earliest ultrasound. If you have another ultrasound later in pregnancy that comes up with a different due date, your due date does not change. Again, the earliest ultrasound is best. And then the last thing, although I keep saying due date because that's what we say, don't get attached to the date, it is not an accurate prediction of exactly when you're going to go into labor. Most women do not go into labor on their due date, so it's really a rough estimate of when you'll go into labor. It's a very accurate estimate of how far along you are in pregnancy. It's very accurate for that, but it is not a good estimate for when you will go into labor. Those are two separate things. Most likely you're going to go into labor after your due date.

: Okay, so that's it for this episode. Were you ever confused about your due date? Have you been confused during your pregnancy? Let me know in the podcast community Facebook group, it's called All About Pregnancy and Birth Podcast Community, or shoot me a DM on Instagram. I'm on Instagram at Dr. Nicole Rankins. And be sure to subscribe to the podcast in iTunes or wherever you listen to podcasts. And if you feel so inclined, you know I would love it if you leave an honest review on iTunes. I can give you a shoutout on a future show. It also helps other women find the show.

: Now next week on the podcast, it's a birth story episode and Brandy is going to come on and she will share her experience with an unplanned cesarean birth and a couple other things that didn't go exactly how she thought she would have liked them to go during her birth. However, she really makes the best of it. So come on back next week. And until then, I wish you a healthy and happy pregnancy and birth.

: Today's episode is brought to you by Women's Wellness Coaching by Dr. Nicole Calloway Rankins. Head to www.ncrcoaching.com to check out my free one hour mini course on how to make your birth plan as well as my comprehensive online childbirth education class, The Birth Preparation Course, with over eight hours of content and a private course community. The Birth Preparation Course will leave you knowledgeable, prepared, confident, and empowered going into your birth. Head to www.ncrcoaching.com to learn more.