The normal length of pregnancy is from 37 to 41 weeks. Postmaturity refers to any baby born after 42 weeks gestation or 294 days past the first day of the mother's last menstrual period. Less than 6 percent of all babies are born at 42 weeks or later. Other terms often used to describe these late births include post-term, postmaturity, prolonged pregnancy, and post-dates pregnancy.
It is not known why some pregnancies last longer than others. Postmaturity is more likely when a mother has had one or more previous post-term pregnancies. Sometimes a mother's pregnancy due date is miscalculated because she is not sure of her last menstrual period. A miscalculation may mean the baby is born earlier or later than expected.
Postmature babies are born after the normal length of pregnancy. The placenta, which supplies babies with the nutrients and oxygen from the mother's circulation, begins to age toward the end of pregnancy, and may not function as efficiently as before. Other concerns include the following:
Amniotic fluid volume may decrease and the fetus may stop gaining weight or may even lose weight.
Risks can increase during labor and birth for a fetus with poor oxygen supply.
Problems may occur during birth if the baby is large.
Postmature babies may be at risk for meconium aspiration, when a baby breathes in fluid containing the first stool.
Hypoglycemia (low blood sugar) can also occur because the baby has already used up its glucose-producing stores.
The following are the most common symptoms of postmaturity. However, each baby may show different symptoms of the condition. Symptoms may include:
Dry, loose, peeling skin
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 during pregnancy into the amniotic fluid)
More alert and "wide-eyed"
Symptoms of postmaturity may resemble other conditions or medical problems. Always consult your baby's doctor for a diagnosis.
Postmaturity is usually diagnosed by a combination of assessments, including the following:
Testing may be done for a post-term pregnancy to check fetal well-being and identify problems. Tests often include ultrasound, nonstress testing (how the fetal heart rate responds to fetal activity), and estimation of the amniotic fluid volume.
The decision to induce labor for post-term pregnancy depends on many factors. During labor, the fetal heart rate may be monitored with an electronic monitor to help identify changes in the heart rate due to low oxygenation. Changes in a baby's condition may require a cesarean delivery.
Special care of the postmature baby may include:
Accurate pregnancy due dates can help identify babies at risk for postmaturity. Ultrasound examinations early in pregnancy help establish more accurate dating by measurements taken of the fetus. Ultrasound is also important in evaluating the placenta for signs of aging.