Health Encyclopedia


What is postmaturity?

The normal length of pregnancy is from 37 to 41 weeks. Postmaturity is a word that doctors use to describe babies born after 42 weeks (294 days past the first day of the mother's last menstrual period). Very few babies are born at 42 weeks or later. Other words often used to describe these late births include post-term, postmaturity, prolonged pregnancy, and post-dates pregnancy.

What causes postmaturity?

Doctors don't know why some pregnancies last longer than others. Postmaturity is more likely to happen when a mother has had a post-term pregnancy before. Sometimes a mother's pregnancy due date is off because she is not sure of her last menstrual period. Getting the date wrong may mean the baby is born earlier or later than expected.

Why is postmaturity a concern?

Postmature babies are born after the normal length of pregnancy. The placenta, which supplies babies with the nutrients and oxygen from the mother's blood, begins to age toward the end of pregnancy. It may not function as efficiently as before. Other concerns are:

  • Less amniotic fluid. This may stop the baby from gaining weight or may even cause weight loss.

  • Poor oxygen supply. Babies that don't get enough oxygen may have problems during labor and delivery.

  • Large size. A large baby may cause problems for the mother during labor and delivery.

  • Meconium aspiration. Babies who stay in the womb longer are more likely to breathe in fluid containing their first stools (meconium).

  • Hypoglycemia (low blood sugar). This happens when the baby has already used up its glucose-producing stores.

What are the symptoms of postmaturity?

Each baby may show different symptoms of postmaturity. Some of those symptoms are:

  • Dry, loose, peeling skin

  • Overgrown nails

  • Abundant scalp hair

  • Visible creases on palms and soles of feet

  • Minimal fat deposits

  • Green, brown, or yellow coloring of skin from meconium staining (the first stool passed while in the womb)

  • More alert and "wide-eyed"

Symptoms of postmaturity sometimes look like other conditions or medical problems. Always see your baby's health care provider for a diagnosis.

How is postmaturity diagnosed?

Your baby's health care provider will check:

  • Your baby's physical appearance

  • The length of your pregnancy

  • How old your baby appears to be

Treatment of postmaturity

Your baby's health care provider will check your baby's health and look for any problems. Tests may need to be done. These may include:

  • Ultrasound

  • Nonstress testing (how the fetal heart rate responds to fetal activity)

  • Checking the amount of amniotic fluid

Your health care provider may decide to start your labor early, depending on several things. During labor, your baby's heart rate may be watched with an electronic monitor. This will help to spot changes in the heart rate due to low oxygen levels. Changes in your baby's condition may require a cesarean delivery.

Special care of the postmature baby may include:

  • Checking for breathing problems caused by meconium (baby's first bowel movement) aspiration

  • Blood tests for low blood sugar (hypoglycemia)

Prevention of postmaturity

Knowing your due date is the best way to know if your baby may be postmature. Ultrasound tests early in pregnancy can help your health care provider figure out the age of your baby by check his or her size. Ultrasound is also a good way to check the placenta for signs of aging.

Medical Reviewers:

  • MMI board-certified, academically-affiliated clinician
  • Trevino, Heather M., BSN, RNC