An estimated due date (EDD) is an approximate calculation, and only about 4 percent of babies are born on this date. This means that the other 96 percent of births occur either before or after the EDD. However, there is a common misconception that the due date is a definitive deadline for when the baby must be born. In reality, a pregnancy is not considered “post-term” or overdue until after 42 weeks, according to the American College of Obstetricians and Gynecologists (ACOG).
ACOG guidelines state that most women give birth between 38 and 42 weeks of pregnancy, with very few babies being born exactly on their due dates. It is normal for a healthy pregnancy to result in birth up to 3 weeks before or 2 weeks after the due date. While the average pregnancy lasts between 38 and 42 weeks, some pregnancies may extend beyond 42 weeks and still result in the birth of a healthy baby. The longest recorded pregnancy lasted 375 days, or approximately 53 weeks and 4 days.
As of October 2013, ACOG updated its definitions for pregnancy terms to provide more precise guidelines:
- Preterm: Babies born on or before 36 weeks 6 days of gestation.
- Early Term: Babies born between 37 weeks and 38 weeks 6 days.
- Full Term: Babies born between 39 weeks and 40 weeks 6 days.
- Late Term: Babies born between 41 weeks and 41 weeks 6 days.
- Post-term: Babies born at 42 weeks or later.
These changes were made to help reduce the number of early deliveries that are scheduled for non-medical reasons.
For example, if a due date is January 7, labor could begin as early as December 24 or as late as January 27, and the pregnancy would still be within the average length. Accurate calculation of the due date is important, and for women who know their ovulation date, such as those tracking their cycle with methods like the Fertility Awareness Method or using ovulation predictor kits, the EDD can be calculated more precisely. For others, the EDD may be less accurate by a few days to a few weeks, and healthcare providers can use additional methods to refine the estimate.
While the risk of complications does increase slightly after 42 weeks of pregnancy, ongoing monitoring by healthcare providers typically ensures that a longer pregnancy remains safe. Most women who reach or surpass 42 weeks of pregnancy go on to deliver healthy babies. Therefore, a pregnancy that extends beyond the due date does not necessarily indicate a problem; some pregnancies simply take longer to reach full term. Some buns just need a little extra time in the oven!
References
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