What's in a due date?

We explain the facts surrounding your baby's estimated date of arrival.

Ah, the due date. Most pregnant women look longingly toward that one day singled out by their doctor, circling it in red on the calendar and counting down the weeks until the big day.

Of course, very few babies are actually born on their due date—in fact, fewer than 5 percent of babies make their entrance on the circled day. Here’s what you need to know about those monumental 24 hours your hopes are resting on.  

How is a due date figured?

In the old days, it all depended on mom’s memory—when was the date of your last period? Count back three months from the first day of your last menstrual cycle, then add seven days, and that’s your estimated date of delivery. So if your last period began on March 21st, your due date would be December 28th (back three months, plus seven days).

Needless to say, this can be tough to figure for moms with irregular cycles. Technology is here to save us, though, in the form of an ultrasound machine. Doctors and ultrasound technicians can measure the size and development of a fetus to determine it’s gestational age, therefore providing a timeline for arrival. Your due date might actually change at some point during your pregnancy if your health care provider realizes that the original estimate was a little off. But estimate is the key word here—there’s no way of telling when baby is going to make his way into the world, so your due date might come and go with no sign of baby—or your baby may already be snuggled cozily in mommy’s arms.

Early, late, right on time

If you feel labor pains 12 days before your due date, don’t panic—your baby isn’t premature. A child is considered full term anywhere from 37 to 42 weeks gestation. Some obstetricians will induce anywhere after the 37-week mark (or schedule a C-section, if it’s been determined that you will need one), but others might wait until closer to 40 weeks to get things in motion. However, almost all doctors will induce if your baby hasn’t arrived by 42 weeks. Since the due date is just an educated guess, it’s reasonable to assume that rather than overstaying his welcome, your baby simply isn’t ready to make an exit.
 
But after the 42-week mark, chances of complications during delivery increase, giving most obs and midwives reason enough to jump-start your labor. (However, hitting the 42nd week with no sign of baby isn’t necessarily a cause for concern—according to the American College of Obstetrics and Gynecology, 95 percent of post-term babies are delivered without complication.)

One thing’s for sure—accurate or not, that due date gives mamas something to look forward to during those 40 (or 41, or 42…) long weeks. Here’s to hoping you have a happy delivery!