What is postdate pregnancy?

The length of a normal pregnancy is 38 to 42 weeks from the first day of the last menstrual period. A postdate pregnancy is a pregnancy that lasts longer than 42 weeks. Because there are some very serious risks for both the mother and the baby, the doctor will follow a postdate pregnancy closely.

How does it occur?

Ten percent of all pregnancies are postdate. Most of the time this is because the due date is incorrect. In other cases pregnancies just last longer than normal. Why some pregnancies continue past their due dates is not well understood.

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How is it diagnosed?

You and your doctor must first accurately date your pregnancy. It is much easier to calculate an accurate due date early in the pregnancy. This is one reason you need prenatal care early in your pregnancy.

The doctor 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.

How is it treated?

If you go past your due date, the concern is that the placenta is aging. It may no longer be providing enough oxygen and nutrients to your baby.

There are several ways to check the health of an overdue baby starting at 40 weeks:

• a kick count, where you count movements your baby makes during a prescribed length of time
• electronic fetal monitoring (nonstress test)
• ultrasound evaluation (biophysical profile)
• ultrasound measurement of the amount of amniotic fluid.

If the health of your baby is unclear or dates are uncertain, your doctor may do an amniocentesis. For this test some amniotic fluid is taken from your uterus. Tests of the fluid can show how mature your baby's lungs are.

All of this information helps your doctor determine whether it is safe to wait for labor or if it is time to induce labor to deliver the baby.

• At 41 weeks your doctor may induce labor, especially if your cervix has ripened and is ready for delivery. (Inducing labor means starting it artificially, such as with medication.)
• If the baby appears to be healthy and not in danger, your doctor may check you regularly and wait for labor to begin naturally.
• If the baby appears to be in danger, labor may have to be induced, or the baby may be delivered by cesarean section.

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What are the risks?

• If the pregnancy continues, your baby may not receive enough oxygen or nutrients from the blood of an aging placenta. This could stop the baby's growth, damage the baby's brain, or even kill the baby.
• Meconium is a greenish substance that builds up in your baby's bowels and is normally discharged shortly after birth. If it is discharged into the amniotic fluid before birth, the baby might inhale it. Inhalation of meconium into the lungs can cause severe breathing problems for the baby at birth. If meconium is found, your baby will be monitored very closely.

What can be done to prevent harm to my baby?

The most important thing you can do to have a healthy baby is to see a doctor and begin prenatal care as soon as you think you are pregnant.

If you have passed your due date, your doctor may avoid possible harm to your baby by inducing labor as your pregnancy nears 41 weeks. Also, if your cervix is not yet ready for labor, you could have problems such as prolonged labor and infection. Delivery by cesarean section might become necessary. Make sure that you discuss all risks and options with your doctor before delivery.

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Information provided by UMHS perinatal education committee March, 2005