Most pregnancies last 37 to 42 weeks, but some take longer. If your pregnancy lasts more than 42 weeks, it is called post-term (past due). This happens in a small number of pregnancies.
While there are some risks in a post-term pregnancy, most post-term babies are born healthy. Your doctor can do special tests to check on the health of your baby. Keeping a close eye on the baby's health will help increase the chance of good outcomes.
Many women who go past 40 weeks are not really post-term. Their due date was just not calculated correctly. After all, a due date is not exact, but an estimate.
Your due date is estimated based on the first day of your last period, the size of your uterus (womb) early in your pregnancy, and with an ultrasound early in pregnancy. However:
When a pregnancy truly is post-term and goes past 42 weeks, no one knows for sure what causes it to happen.
If you have not given birth by 42 weeks, there are greater health risks for you and your baby.
The placenta is the link between you and your baby. As you pass your due date, the placenta may not work as well as before. This could lessen the amount of oxygen and nutrients that the baby gets from you. As a result, the baby:
Other problems that may occur:
Any of these problems can increase the need for a C-section.
Until you reach 41 weeks, your doctor may not do anything unless there are problems.
If you reach 41 weeks (one week overdue), your doctor will do tests to check on the baby. These tests include a non-stress test and biophysical profile (ultrasound).
When you reach between 41 and 42 weeks, the health risks to you and your baby become even greater. Your doctor will likely want to induce labor. In older women, especially older than 40, it may be recommended to induce labor as early as 39 weeks.
When you have not gone into labor on your own, your doctor will help you start. This may be done by:
You will only need a C-section if:
Farinelli CK, Wing DA. Abnormal labor and induction of labor. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2012:chap 14.
Updated by: Cynthia D. White, MD, Fellow American College of Obstetricians and Gynecologists, Group Health Cooperative, Bellevue, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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