An estimated due date is just that, an estimate. Only about 4 percent of babies are actually born on their due dates. That means that the other 96 percent are born either before or after their EDD. However, some expectant mothers and even doctors think that a due date is the date that the baby must be born by. For some reason, too many people think that a pregnancy is post date at 40 weeks. The American Congress of Obstetricians and Gynecology (ACOG) disagrees.
According to ACOG’s recommendations for obstetricians, a pregnancy is not post date until after 42 weeks. ACOG furthermore states: “Most women give birth between 38 and 42 weeks of pregnancy. But very few babies are born on their due dates. It is normal to give birth as much as 3 weeks before or 2 weeks after your due date.” In other words, although the average pregnancy ends with the birth of a baby between the first day of 38 weeks and the last day of 42 weeks, some perfectly healthy pregnancies last beyond 42 weeks. In fact, the longest pregnancy on record lasted a whopping 375 days, or 53 weeks 4 days!
Update: Prior to October 2013, ACOG defined term as babies born between week 37 and week 42 of gestation. The most recent update considers a pregnancy term between 37 weeks and 41 weeks 6 days. Babies born on or before 36 weeks 6 days are consider preterm or premature. Babies born between 37 weeks and 38 weeks 6 days are considered early term. Babies born between 39 weeks and 40 weeks 6 days are considered full term. Babies born between 41 weeks and 41 weeks 6 days. Babies born on or after 42 weeks are consider post-term or post-date. ACOG made changes to the definition of term to help prevent births that are being scheduled early for non-medical reasons.
My due date is January 7. However, I know that I could give birth as early as December 24 or as late as January 27. My pregnancy would still be considered of average length. Furthermore, I am absolutely positive about the date of conception for my pregnancy. I had been charting my cycle using the Fertility Awareness Method and using an ovulation predictor kit (OPK). I know that I ovulated on April 16, so the due date that I calculated myself falls at exactly 40 weeks. For women who are unsure about their ovulation date, their estimated due date may be off as little as a few days to as much as a few weeks. Medical professionals can use other methods to make an EDD more accurate; however, the best starting point is the date of ovulation.
When a pregnancy extends beyond the end of week 42, the risk of complications do rise. But only slightly. So long as a midwife or doctor and the expectant mother keeps an eye on the baby and the pregnancy, a longer pregnancy is generally not a problem. In fact, most women who are considered post date go on to give birth to healthy babies. In other words, should my firstborn not decide to grace us with his or her presence until after January 27, my first reaction will not be panic or worry. The average pregnancy lasts between 37 weeks and 41 weeks 6 days. ACOG does not consider a pregnancy overdue until 42 weeks. Some buns just need a little extra time in the oven!
ACOG: Post Date Is Past 42 Weeks: http://birthwithoutfearblog.com/2011/08/22/what-acog-has-to-say-about-due-dates/
Medicine: Prodigious Pregnancy: http://www.time.com/time/magazine/article/0,9171,797153,00.html
Ob-Gyns Redefine Meaning of “Term Pregnancy”: http://www.acog.org/About-ACOG/News-Room/News-Releases/2013/Ob-Gyns-Redefine-Meaning-of-Term-Pregnancy
Pregnant Belly: http://commons.wikimedia.org/wiki/File:Pregnant_woman2.jpg