Late-Term and Postterm Pregnancy

ByJessian L. Muñoz, MD, PhD, MPH, Baylor College of Medicine
Reviewed/Revised Sept 2024
VIEW PROFESSIONAL VERSION

    Late-term pregnancy is defined as pregnancy between 41 weeks and 41 weeks and 6 days. 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.

    On average, pregnancy lasts 280 days (40 weeks) from the first day of the last menstrual period. In most pregnancies that go a little beyond, up to 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 pregnancy increases risks for the pregnant woman and fetus, such as

    Meconium can sometimes be inhaled before or during delivery, causing the baby to have difficulty breathing shortly after birth. This disorder is called meconium aspiration syndrome.

    A postmature fetus may have dry, peeling skin, overgrown nails, a large amount of scalp hair, deep creases on the palms and soles, little body fat, and skin that is stained green or yellow by meconium.

    Did You Know...

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

    To diagnose a postterm pregnancy, doctors must accurately determine the due date. If women have regular menstrual cycles, doctors can calculate the due date based on when their last menstrual period was. But the most accurate way to date a pregnancy is ultrasound, especially if done during the first 12 weeks of pregnancy.

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

    Labor is started (induced) if the fetus is having problems or amniotic fluid has decreased too much. Even if there are no obvious problems, doctors consider inducing labor at 41 weeks. Typically after 42 weeks, labor is induced.

    Sometimes cesarean delivery is required.

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