Postdate Pregnancy

What is a postdate pregnancy?

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.

How does it occur?

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.

How is it diagnosed?

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.

How is it treated?

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:

• checking the baby’s movements by doing a kick count, which means that you count movements your baby makes during a certain length of time
• electronic fetal heart rate monitoring (nonstress or contraction stress test)
• an ultrasound test called a biophysical profile
• ultrasound measurement of the amniotic fluid

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.

• If the baby appears to be healthy and not in danger, your provider may check you regularly and wait for labor to begin naturally.
• If tests show that there is a developing problem, labor may have to be induced, or the baby may be delivered by C section.
• At 42 weeks your provider may induce labor, especially if your cervix has ripened and is ready for delivery.

What are the risks of postdate pregnancy?

Examples of risks to the baby include:

• If the pregnancy continues, your baby may not get enough oxygen or nutrients from the placenta. This could stop the baby's growth, harm the baby's brain, or even cause death of the baby with a stillbirth.
• The baby may make its first bowel movement inside the uterus, which happens more often in postdate pregnancies. The material is called meconium. Most of the time meconium is first passed by the baby after it is born. However, if it happens in the amniotic fluid before birth, the baby can breathe the meconium into the lungs which could cause serious breathing problems after birth.
• You may develop a problem called oligohydramnios, which means too little amniotic fluid around the baby. It can lead to problems during labor and delivery.
• The baby may have low blood sugar.
• Babies delivered postdate have a higher chance of needing to be cared for in a special intensive care unit for newborns.

What can be done to lower the chances of harm to the baby?

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.