So, your due date has come... and gone...
First of all, let's be clear about EDDs, or Estimated Due Dates (also called Estimated Date of Delivery). You can tell from my italics that the term estimated is critically important in understanding due dates!
Where do due dates come from?
An EDD is calculated as 280 days past the first day of your last period. EDDs can also be determined by measuring your baby during an early ultrasound, which is a more reliable method.
Here's the thing about EDDs calculated as LMP (last menstrual period) + 280 days. There's lots of room for error with that approach. Many women misremember the first day of their last period and do their best to guess. Even if you're sure of your LMP, using this day to calculate a due date assumes that you ovulate on day 14 of your cycle and have 28 day cycles. The whole idea of EDD = LMP +280 days is also based on little sound evidence. Back in 1744, Dr. Boerhaave, a professor from the Netherlends, looked at data from 100 women and concluded that most people gave birth within about 280 days of their LMP (although he didn't specify whether LMP meant the first or last day of the menstrual period. In 1812, Dr. Carl Naegele further popularized this process of EDD calculation, but he used the last day of the period as the LMP. In the 1900s, obstetric textbooks started using the first day of the period as the LMP.) So the very process by which due dates are determined isn't very specific, and is based on very limited data!
It's tricky, then, if we take an EDD to mean much more than an estimate of when baby might arrive. As Rebecca Dekker of Evidence Based Birth concludes,
"Based on the best evidence, there is no such thing as an exact “due date,” and the estimated due date of 40 weeks is not accurate. Instead, it would be more appropriate to say that there is a normal range of time in which most people give birth. About half of all pregnant people will go into labor on their own by 40 weeks and 5 days (for first-time mothers) or 40 weeks and 3 days (for mothers who have given birth before). The other half will not."
Instead of fixating on a due date, you may prefer to refer to your EDD as a "guess date," or think more about your "due month" than a specific day.
Now that we have a better idea of where due dates come from and what they do--and don't--mean, let's talk about being "overdue."
As evidenced above, there's nothing magical about the 40-week mark. It's actually more likely that, if you wait to begin labor on your own, you'll give birth a few days past your EDD than on the due date itself. Babies aren't considered "late term" until you reach the 41 week mark, and "post term" doesn't apply until babies are past 42 weeks gestation. Induction for being "overdue" isn't recommended until you're at least 41 weeks pregnant.
It's almost as if pregnancy is trying to teach us the vital parenting skill of patience.
So, what's the takeaway?
Pregnancies aren't like final projects or rent due dates. No points are deducted or fees added for going past your due date. A due date just gives an estimate of when your baby is likely to be born, but really doesn't mean anything definitive. My advice is to schedule a week full of pampering and things to look forward to on your due date and the few days past it. Plan on getting food from your favorite restaurant, going for a walk in your favorite spot, connecting with friends or family. Practice some of those comfort measures that will come in handy during labor. Snuggle up with some great birth books. And know that your baby and your body will work together to signal when it's the right time for baby to come!
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This whole business of calculating due dates and going past your due date is really quite complex. Now that you've been introduced to the topic, I recommend digging into it more with these two articles from Evidence Based Birth: The Evidence on: Due Dates and The Evidence on: Inducing for Due Dates.
Hi, I'm Sara. I'm a childbirth educator and birth + postpartum doula serving Utah county. I'm a twin mom (plus one!), natural VBACer, and birth lover!