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 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 due to shoulder dystocia (the fetus's shoulder lodges against the woman's pubic bone, and the baby is caught in the birth canal)
- The need for cesarean delivery or operative vaginal delivery (with forceps or a vacuum extractor)
- Abnormal growth of the fetus (for example, an abnormally large fetus or abnormally small fetus)
- Too little amniotic fluid around the fetus (oligohydramnios)
- Problems with blood flow to the fetus, depriving the fetus or newborn of oxygen
- Passage of meconium (the fetus’s first stool) before delivery
- A newborn who needs care in a neonatal intensive care unit
- Death of the fetus or newborn
- Tears in the area between the opening of the vagina and anus (perineum)
- Excessive bleeding at delivery (postpartum hemorrhage)
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...
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 ultrasonography 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.