A postdate pregnancy is generally considered to be a pregnancy that lasts longer than 42 weeks.
The average length of a normal term pregnancy is 37 to 42 weeks from the first day of the last menstrual period. The due date is considered to be at 40 weeks. When a pregnancy lasts longer than 40 weeks it is said to be a postterm pregnancy. The chances of a problem for the baby slowly start to increase starting around 41 weeks, so your healthcare provider may decide to watch your pregnancy more closely if you do not deliver by your due date. The risks for both mother and baby are much higher after 42 weeks. If you are still pregnant after 42 weeks, your healthcare provider will follow your pregnancy very closely or recommend delivery.
Seven percent of all pregnancies are postterm. Sometimes this is because the due date is wrong. In other cases pregnancies just last longer than average. Why some pregnancies go past their due dates is not well understood.
You and your healthcare provider must first accurately date your pregnancy. It is much easier to calculate an accurate due date early in the pregnancy. This is one of the reasons you need to start prenatal care early in your pregnancy.
Your provider uses several kinds of information to calculate your due date, including the date of your last menstrual period and how regular your periods are. An ultrasound scan may be used to measure the baby and estimate the due date. This estimate is usually accurate within 7 to 10 days if the ultrasound scan is done during the first half of the pregnancy. Ultrasound measurements may be used later in the pregnancy to help determine a due date, but they may be less accurate.
If you go past your due date, the concern is that the placenta is getting old and may not work as well as it needs to. It may no longer be able to bring enough oxygen and nutrients to your baby.
There are several ways to check the health of an overdue baby:
These tests are often started around 41 weeks. Information from these tests helps your provider determine whether it is safe to wait for labor, if it is time to induce labor to deliver the baby, or if a cesarean section (C-section) is needed.
Examples of risks to the baby include:
If you have passed your due date, your healthcare provider may consider inducing labor as your pregnancy nears 41 to 42 weeks. However, there are risks if the baby is delivered too early and is not ready to be born. Also, if your cervix is not ready for labor, you could have problems such as prolonged labor and infection. Delivery by C-section might become necessary. Make sure that you discuss the risks and options of delivery with your provider.