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Postterm Pregnancy

By Julie S. Moldenhauer, MD

Postterm pregnancy refers to gestation that lasts 42 wk. Antenatal surveillance should be considered at 41 wk. Induction of labor should be considered after 41 wk and is recommended after 42 wk.

Accurate gestational age estimation is essential in making a diagnosis of postterm pregnancy. In women with regular, normal menstrual cycles, gestational age can be estimated based on the first day of the last normal menstrual period. If dating is uncertain or inconsistent with menstrual dating, ultrasonography early in gestation (up to 20 wk) is the most accurate with accepted variation of +/ 7 days. Later in gestation, the variation increases to +/ 14 days at 20 to 30 wk gestation and +/ 21 days after 30 wk.

Postterm pregnancy increases risks for the woman and fetus. Risks include

  • Abnormal fetal growth (macrosomia and dysmaturity syndrome)

  • Oligohydramnios

  • Meconium-stained amniotic fluid

  • Nonreassuring fetal test results

  • Fetal and neonatal death

  • Need for neonatal intensive care

  • Dystocia (abnormal or difficult labor)

  • Cesarean delivery

  • Perineal lacerations

  • Postpartum hemorrhage

Postmaturity refers to the condition of the fetus that results when the placenta can no longer maintain a healthy environment for growth and development, usually because the pregnancy has lasted too long. The fetus may have dry, peeling skin, overgrown nails, a large amount of scalp hair, marked creases on the palms and soles, lack of fat deposition, and skin that is stained green or yellow by meconium. Meconium aspiration is a risk.

Antenatal surveillance should be considered at 41 wk; it involves one of the following:

  • Nonstress testing

  • Modified biophysical profile (nonstress testing and assessment of amniotic fluid volume)

  • A full biophysical profile (assessment of amniotic fluid volume and fetal movement, tone, breathing, and heart rate)

Treatment

  • Induction of labor and delivery

If there is evidence of fetal compromise or oligohydramnios, delivery is required. Induction of labor can be considered at 41 to 42 wk, particularly if the cervix is favorable, and is recommended after 42 wk.

* This is the Professional Version. *