Due Dates - How Accurate Are They?

This has to be one of the worst things pregnant women are subjected to. The ominous due date.

The entire pregnancy can be beautiful – complete with supportive friends and family celebrating you and the baby that is soon to arrive – but then as the due date approaches and arrives and passes, there can be a dramatic dark shift with constant comments, questions, phone calls and messages – “Is the baby here yet? Is everything ok? Did you have that baby yet?”.

It’s beyond annoying, inviting fear and anxiety into a time that should be calm, peaceful and supported.

I think it’s really common too for mothers to think “what’s wrong with me?” or “what am I doing wrong?” if their baby doesn't arrive "on time" – adding guilt, now, into it all too.

When you were first given that date it seemed magical. Of course, you told yourself, it probably won’t be on that day exactly but it will be around that time. And that date stuck.

Not just for you – but for all of those around you. Your family, your friends. Your care provider.

From then on, it's all about waiting for that day to come – you prepare – you wait with great anticipation - the day approaches and you’re ready and excited. But what happens when 2 days pass, or 8 – or 11…what if it’s 15?? Or more. What happens then?

The fear, the impatience, the questions from friends, the family, the comments from strangers at the grocery store “wow – you’re huge! Are you having twins??”…. so much stress! (keep in mind that stress hormones can hold a labor up or keep it from starting).

So the question for me is WHY? Why do we choose to torture ourselves unnecessarily? Completely unnecessarily once we understand the science – or lack of – behind the EDD or Estimated Date of Delivery.

I get that in a medicalized birth system, it helps to have an approximate date of birth, but knowing how inaccurate the system is that is used to arrive at that date, combined with the potential interventions that revolve around it along with the fear, stress and impatience experienced by mothers because of it – well, it has really all gotten out of control. And the sad thing is - it really doesn’t need to be this way.

Let’s begin with the fear of going “over due”. Which technically is over 42 weeks. The assumption is that it is risky.

This is an important preliminary point. The answer is yes, there is a risk. Let’s look at it..

The risk of going past 42 weeks is that the rate of having a stillbirth increases. Which, I know, sounds horrifying.

Statistically, by going over 42 weeks the risk is 4 to 7 deaths per 1000 deliveries, as opposed to 2 to 3 deaths per 1000 deliveries in women who deliver between 37 and 42 weeks. This is one of those studies that people could cite as showing that the risk of death doubles if you go over 42 weeks. Which is true. Very slight increase, but justifiably doubled.

Yet, because of the higher risk, care providers will then begin some interventions. And the irony, is that the amount of interventions that are performed with the purpose of reducing that risk, carry significant risks themselves.

Let’s take induction. Many times it’s the first step that is taken as that date approaches (on a side note, the 42 weeks has actually now been replaced with 41 for most medical care providers and in 2018 the rules also changed allowing for elective inductions whereas before there had to be a medical reason for performing one).

I want to share this from the Mayo Clinic addressing the risks of induction:

Labor induction carries various risks, including:

• Failed induction. (About 75 percent of first-time mothers who are induced will have a successful vaginal delivery)
• Low heart rate.
• Infection.
• Uterine rupture.
• Bleeding after delivery.

Also, once interventions begin, the chances of having a surgical birth (C-Section) increase.

Having a surgical birth carries some hefty risks (and the more you have, the greater the risk). There are many really well written articles and posts all about this! So I’ll save everyone’s time and just give the bottom line. It will go fast…

First let me say this – a C-section is a wonderful tool when it’s really necessary. I’m citing this information below for the purposes of understanding the risks involved when it isn’t necessary and may result in a cascade of other induction interventions.

First this again from the Mayo Clinic…

Risks of Cesarean Section

• Infection. After a C–section, you might be at risk of developing an infection of the lining of the uterus (endometritis).
• Postpartum hemorrhage.
• Reactions to anesthesia.
• Blood clots.
• Wound infection.
• Surgical injury.
• Increased risks during future pregnancies.

This is a quote from the European WHO

“Maternal mortality and morbidity is approximately five times greater with caesarean than with vaginal birth: specifically, the risks of hemorrhage, sepsis, venous thromboembolism and amniotic fluid embolism.”

And then this from Medscape:

“Approximately one third to one half of maternal deaths after cesarean delivery being directly attributable to the operative procedure itself.”

Add to this the 100 percent guaranteed risk of bathing the baby in stress hormones just as they’re preparing to enter the world and the message that they receive of “I don’t know if it’s safe here”. That’s a big message to a vulnerable baby that carries life long implications.

Something is WRONG here.

Out of our fear of a SLIGHTLY increased risk of stillborn birth – real yet rare – we’ve not only adopted practices that carry greater risk factors, we’ve normalized them.

And we’re ignoring and/or accepting greater risks as a result.

Although I don’t think most people make a conscious decision to comply with these practices. I don’t think many people have even had the idea to think past the common collective belief – that going over your due date is very dangerous.

I think that most people just inherently trust the doctors. The professionals. That they are making decisions based on what is best for me and my baby. That they know the science and that they practice medicine accordingly.

I think that it’s very likely, that the doctors themselves don’t even know why things are the way they are. And I don’t know if its worth it to deconstruct why it’s come to be this way. What I do believe is worth it though, is to educate ourselves. And then to retain the power of your birth by making your own damn decisions.

I’ve so over this insanity! With mothers believing that they don’t have the authority, permission or ability to curate this magnificent rite of passage for themselves.

It can actually be really easy. All we have to do is to decide what it is that we want – and to choose a more gentle way.

Not only should you not be afraid of the baby coming late – you could be celebrating these last days of pregnancy! You could be chilling out – eating chocolate while binge watching old movies. Or writing your life story for your child while using their little body inside you as a desk.

You could be glad that when your baby does arrive, that their lungs are going to work the way they need to.

And…don’t forget – you’re getting ready to do a really big thing! The best thing you can do is to relax!

There's more to it though....so I'm going to go technical for a bit here – but I am excited to share this…

I want to break this whole thing down - the Due Date that dictates and is the precursor to the interventions, as it is shrouded in confusion and mystery – even to perinatal experts believe it or not.

First lets take GESTATIONAL AGE vs. FETAL AGE. These are not the same thing.

Gestational Age is based on the first day of your last menstrual period (LMP) and with the GA, the due date is calculated as 280 days – or 40 weeks from the first day of your last period.

This is different than Fetal Age, which is based on the actual age of the baby from the conception date and is 266 days – or 38 weeks.

Typically, when someone finds out they’re pregnant, they will be given an EDD based on the Gestational Age.

However, the potential inaccuracy of this is obvious. Not everyone remembers the exact date of the first day of their last LMP. Even if you’re only off by a day or 2, the due date will reflect that. In other words – your due date which will be etched in stone and used to make big decisions that you probably don’t want to have to make, is determined on your perfect memory, and if you’re 3 or 8 days off, your due date will reflect that.

Although ovulation/cycle apps are being used more now which is a good way to know that LMP – but only if you consistently stay on top of it and/or if you have perfect consistent cycles. I never could keep up with the app I tried as my cycles were so irregular.

There’s also the issue of implantation bleeding (usually occuring around 2 weeks after conception) which is often mistaken for a period. Easy to do, especially if your periods are irregular - resulting in two weeks off if you inadvertently count it as your LMP.

The GA is also based on a firm 28 day cycle which not everyone has. You may have a 32 day cycle. If so, the due date will be off 4 days. So for example, let’s say that you did not know the exact date of your LMP, and your best guess is off by 5 days. Now add on to that the fact that your cycles are 31 days long – right from the beginning you’re 8 days off. Not necessarily that big of a deal at the beginning of your pregnancy. But 8 days at the end of it is significant.

As that date draws near and then passes, interventions will begin being discussed and entertained. Anything from sweeping the membranes to breaking the water, to induction through various methods, to surgical birth (C-section).

Once one intervention happens, the cascade has begun and a simple breaking of the water to “get things going” can easily end up in an unplanned and unwanted C-section. Sometimes breaking the water (amniotic sac) is effective and labor will begin - or a simple sweeping of the membranes (which is quite painful) can work too. But sometimes it doesn't. 

During the last weeks of a pregnancy, mothers are especially vulnerable, I might add. And it can be really difficult to advocate for what you want or don’t want while in that state. So many mothers just go along with whatever they’re told to do, driven by fear and feelings of “I just want this baby out”. You’ll almost do anything to get it all over with. Doing this work for so many years, I’ve seen it many times.

I’m speaking mostly right now to those who are having a medical birth. But homebirth midwives are adhering to these time tables as well and will transfer care of a mother if she goes past 42 weeks. Some states that license home birth midwives do so with a list of regulations – and providing care for a mother who has gone past 42 weeks is many times on that list of what the midwives are not allowed to do.

I even had a free birthing client once who had to fight family members off who were harassing and threatening them as they were entering what they thought was their 43rd week (when we had a conversation together and went over the beginning stages of how they had arrived at their due date in greater detail, they realized that they were probably closer to 40.5 weeks and had a beautiful unassisted birth a few days later).

Keep in mind the Gestational Age is NOT the age of the baby – it is based on the first day of the last period, therefore, it’s more or less 2 weeks off of the actual age of the baby. So when someone says they are 14 weeks pregnant, this is typically the Gestational Age that is given. The baby is not 14 weeks old. It is 12 weeks old - the Fetal Age. So in a typical average pregnancy, the baby actually grows for an average of 38 weeks rather than 40.

We have Dr. Neagle to thank for the advent of the Gestational Age – who, back in the early 1800’s, was the one to determine the average gestation period time and the only indicators he would have had back then would have been the first day of the LMP – so they used that date as the beginning of the pregnancy and added 40 weeks to it to arrive to the approximate due date. This was the beginning of the Gestational Age that is now universally followed and there were no ultrasounds or scans back then to give us technology based data. BUT now that we have it…how accurate is the ultrasound?

The age of the baby determined from an ultrasound is based on measurements. A measurement is taken from the crown of the head, to the bottom part of the butt. And then based on the law of averages that take into account the size of an embryo or fetus at a certain stage, the age is then determined and as the baby grows, the inaccuracy of a due date based on the ultrasound becomes greater.

To understand this method, based on the law of averages and making determinations of age based on size from them, I’ll give you an example that may be easier to understand.

When my oldest son Cam was 3 months old he weighed 20 pounds. I was living in Chattanooga TN at the time and took him for his well baby check up. The doctor was an old fashioned southern doctor and with the longest, most southern drawl you’ve ever heard, he exclaimed to me after weighing Cam 3 separate times to make sure it was right “Whatchu been feedin this boi?” I stood there, a mere 110 pounds, 20 years old “just breastmilk”, I shyly told him. “Well I never in all my years of seeing babies saw one this big – you must have some powerful milk!”. Indeed he was huge for his age. In fact, if we did not know his age, and based on the average weight per age, he should have been 1 year old.

I’m telling you this story to show the gross inaccuracy of basing age on size. Yet this is exactly what is happening with the ultrasound.

In fact, Between 18 and 28 weeks of gestation, the margin of error increases to plus or minus two weeks. After 28 weeks, the ultrasound may be off by three weeks or more in predicting a due date.

So the assumption then is that the earlier the ultrasound, the more accurate. Which is what I thought too until I ran across this study that showed that there are variations in the time of implantation – ie: a fertilized egg may take up to 10 days to implant after conception, significantly effecting the size of the embryo, resulting in yet another variable that can effect the EDD.

Even if you know exactly when conception occurred (which was the case with this study as it consisted entirely of a control group of IVF women) – the exact time of implantation is unpredictable. This study shows that later implantation definitely effects the size of the baby without changing the true age (the conception date determines the beginning of the age of the baby, not the implantation date). Give or take, this gives us another window of potentially an additional 10 days off of the EDD even from the earliest ultrasound.

The irony has always been to me, that the “EDD” that is used by birth professionals literally stands for “ESTIMATED Date of Delivery”. The very definition shows that it is an estimation. So much so, that only 4.4 percent of mothers will actually give birth on the due date they were given.

I haven’t even touched on the fact that the baby initiates labor when it’s lungs are fully developed and ready for life on the outside, or the fact that baby’s gestate differently – some shorter, some longer.

I have to include this by Dr. Jason Gardosi of the Perinatal Institute –

“The baby is likely to come any time between 37 weeks (259 days) and 42 weeks (294 days), a period referred to as “term”, when the baby has reached full maturity – the phrase “due date” is misleading. That makes it sound too accurate – it should really be called an “estimated date”.

I love that.

Regardless of where you are choosing to birth, the overall take away? We need to stop giving these dates so much power.

What would be great would be to offer extra support and encouragement to the mother and family, instead of stressing them out during those last days.

We could celebrate the final stages of the pregnancy like bringing food and snacks to be put in the freezer for the Nest after the birth, or gifts for the mother and siblings – providing a safe emotional field by collectively trusting in the process of birth and infusing the mother with oxytocin which is what she really needs more than anything as she approaches her birthing time.

I recommend to my clients that from the beginning, they never tell anyone a due date – rather a due time. Which is about a month. So for example – you might say “around the end of the year” – or “summer of next year”.

I also have to say that when I was pregnant, I loved those last weeks. I remember people saying “I bet you’re ready to get that baby out” – and I was always kind of shocked at how everyone assumed that I was miserable (it’s funny but by my 7th baby, people were saying that when I was just 6 months pregnant).

But NO – I was happy to be pregnant and to carry my babies all the way to the end knowing that it was better for them. I felt no urgency at all. Which is remarkable because all of my 7 babies were born “over due”. I once went 4 weeks past my due date. Everything was fine.

So this is to you mama! You’re reading this right now and I want to tell you all of this. I want to say – “take a deep breath and relax”… I also want to tell you to trust. And surrender.

During those last weeks, I believe that you really are in a way in labor – an energetic labor that has a big impact on the physical labor that you will be experiencing soon. You can choose to resist this part of labor, but just as it is in the physical labor, there will be pain in that resistance.

When the due date comes and goes – RELAX. TRUST. DO FUN THINGS. Your baby will come out. They always do.

One of the great mysteries that we have in life – is not knowing the exact time of birth or of death. I think it keeps us humble. It gives us an opportunity to respect and deeply trust the process of Life in ways that we may never have the chance to otherwise.

It’s really a beautiful thing – to surrender to and marvel at the mystery and to trust that your baby will come in the perfect time. Although you may have to stay inside away from people and turn your phone off to do it!