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Postterm Pregnancy and Postmaturity

By Julie S. Moldenhauer, MD

A postterm pregnancy is one that lasts 42 weeks or more. In postmaturity , the placenta can no longer maintain a healthy environment for the fetus because the pregnancy has lasted too long.

In most pregnancies that go a little beyond 41 to 42 weeks, no problems develop. However, beyond that time, problems may develop because the placenta often cannot continue to deliver adequate nutrients to the fetus. This condition is called postmaturity. Postterm pregnancies increase the risk of problems such as difficult labor, need for cesarean delivery, and passage of meconium (the fetus’s first stool) before delivery. Meconium can sometimes be inhaled before or during delivery, causing the baby to have difficulty breathing shortly after birth. In the postmature fetus, soft tissues (such as muscle) may waste away. The fetus or newborn may be deprived of oxygen, or die.

Did You Know...

  • If a pregnancy lasts more than 42 weeks, the placenta may malfunction, causing problems for the fetus.

Typically, tests are started at 41 weeks to evaluate the fetus’s movement and heart rate and the amount of amniotic fluid, which decreases markedly in postterm pregnancies. Doctors use ultrasonography and may use electronic fetal heart monitoring to monitor the fetus's status (see page Monitoring the Fetus).

Typically, at 41 weeks or sometimes at 42 weeks, labor is induced. Sometimes cesarean delivery is required.

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