Four Percent Of Babies Born On Due Date

Your due date is just an estimation, and while this can make it hard to plan maternity and paternity leave, your body and your baby know when it’s time for the big day. A new study has shown that the five-week window that most moms deliver in is healthy, normal and to be expected.

Pregnant woman sleeping

When you discover you’re pregnant, you’re given a due date that is calculated based on your last menstrual period. This is based on conventional knowledge that most pregnancies last around 40 weeks -- in other words, when you turn 40 weeks, that day is your due date. However, a new study has determined that the window for safe baby delivery is actually five weeks long, which confirms what many moms and most doctors already knew -- your due “date” window goes from around 37 to 42 weeks.

A due “month,” plus a week

When you calculate your due date, or are handed one by your care provider, you understandably become fixated on that date, even if you are told or already understand that babies can and do arrive before and after this date. As your pregnancy wears on, you’re asked numerous times what your due date is, and you're relegated with stories about moms going “late” and being induced, which can worry you -- what if you go past your due date?

It’s long been known that women can safely deliver anywhere from 37 to 42 weeks (and sometimes beyond), but that has often attributed to not being able to pinpoint the actual date of conception, which can lead to a little give or take when it comes to a “textbook” 40-week pregnancy. The truth is, only four percent of babies make their entry on their due date!

New research

However, when researchers were able to determine the conception date, they discovered the same results -- there is still a five-week window of time where a mom can have her baby. They studied urine samples from 125 moms who had babies in the early 1980s and were able to determine, based on hormone levels, when ovulation took place and therefore when conception occurred. After excluding preterm deliveries, they found the a similar amount of variation -- the length of pregnancy ranged from 38 to 43 weeks from the first day of Mom’s last period.

While this doesn’t change what doctors and moms already know, it does confirm it and sheds a little more light on the variances of human pregnancy. And it really helps to know that your due date isn’t the "end date" and going for two more weeks (or more) is often totally fine.

More on pregnancy

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The mystery of pregnancy due dates
Due date blues? Ways to pass the time

Tags: research

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