What's in a due date?

Ah, the due date. Most moms-to-be look longingly toward the designated day, circling it in red on the calendar and counting down the weeks until baby’s big debut. Oddly enough, however, very few babies are actually born on their due dates. (In fact, fewer than 5 percent of babies make their entrances as predicted.) Here’s what you need to know about the monumental 24 hours your hopes are resting on.
Save the date
In the past, determining a due date depended heavily on mom’s memory. When was your last period? Count back three months from the first day of your last menstrual cycle, then add seven days—that’s your estimated date of delivery. So if your last period began on December 21, your due date would be September 28 (back three months, plus seven days).
Needless to say, this method didn’t bode well for moms with irregular cycles—or foggy math skills. Thankfully, doctors and ultrasound technicians now use an ultrasound machine to measure the size and development of a fetus, determine gestational age, and create a timeline for arrival.
Don’t be surprised if your due date changes at some point during your pregnancy; it’s not uncommon for a healthcare provider to conclude that an original estimate is a little off. After all, estimate is the key word here! There’s no surefire 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 baby may already be snuggled cozily in your arms.
Early, late, right on time
If you feel labor pains 12 days before baby’s due date, don’t panic—they don’t mean your baby will be premature. A child is considered full-term anywhere from 37 to 42 weeks’ gestation. Many obstetricians will induce anytime after the 37-week mark (or schedule a C-section, if it’s been determined that you’ll need one), but others may wait until closer to 40 weeks before they get the ball rolling.
Some expectant moms may be overdue by up to two weeks before their doctors schedule an induction. Since a due date is essentially an educated guess, it’s reasonable to assume that rather than overstaying his welcome, your baby simply isn’t ready to make an exit. In fact, hitting the 42nd week with no sign of baby isn’t necessarily cause for concern—according to the American College of Obstetrics and Gynecology, 95 percent of postterm babies are delivered without complication. After the 42-week mark, however, chances of complications during delivery increase, giving most OBs and midwives reason enough to jump-start labor.
Accurate or not, one thing’s for sure: Due dates give mamas something to look forward to during those 40 (or 41, or 42 … ) long weeks. Let the countdown begin!