Postterm pregnancy refers to gestation at ≥ 42 weeks. Late-term pregnancy is defined as 41 0/7 to 41 6/7 weeks. Antenatal fetal surveillance should be considered at 41 weeks. Induction of labor should be considered after 41 weeks and is recommended after 42 weeks and no later than 42 6/7 weeks.
Accurate gestational age estimation is essential in making a diagnosis of postterm pregnancy. In women with regular menses, gestational age can be estimated based on the first day of the last menstrual period (see American College of Obstetricians and Gynecologists (ACOG): Methods for Estimating the Due Date). If dating is uncertain or inconsistent with menstrual dating, an ultrasound examination early in gestation (up to 20 weeks) can be used.
Postterm pregnancy increases risks for the pregnant patient and fetus. Risks include (1):
Meconium-stained amniotic fluid
Fetal macrosomia, resulting in higher rates of: shoulder dystocia; maternal, fetal, or newborn injury; severe perineal laceration; operative vaginal delivery; or cesarean delivery
Neonatal convulsions
Stillbirth or neonatal death
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 syndrome is a risk.
Antenatal fetal surveillance should be considered starting at 41 weeks; it involves one of the following:
Nonstress test
Modified biophysical profile (nonstress test and assessment of amniotic fluid volume)
A full biophysical profile (assessment of amniotic fluid volume and fetal movement, tone, breathing, and heart rate)
Reference
1. American College of Obstetricians and Gynecologists' Committee on Practice Bulletins: Practice bulletin no. 146: Management of late-term and postterm pregnancies. Obstet Gynecol. 2014;124(2 Pt 1):390-396. doi:10.1097/01.AOG.0000452744.06088.48
Management of Late-Term and Postterm Pregnancy
Induction of labor
Sometimes cesarean delivery
If there is evidence of fetal compromise or oligohydramnios, delivery is required. Induction of labor may be considered at 41 to 41 6/7 weeks, particularly if the cervix is favorable, and is recommended after 42 weeks and no later than 42 6/7 weeks.
Cesarean delivery is not indicated solely for late-term or postterm pregnancy, but may be required for typical obstetric reasons, such as breech presentation, fetal heart rate abnormalities, labor arrest disorders, or maternal medical issues.
Key Points
Accurate gestational-age estimation is essential in making a diagnosis of postterm pregnancy; if menstrual dating is uncertain, an ultrasound examination early in gestation (up to 20 weeks) can be used.
Consider antenatal fetal surveillance (eg, nonstress test, biophysical profile) starting at 41 weeks.
If there is evidence of fetal compromise or oligohydramnios, delivery is required.
Consider inducing labor at 41 to 42 weeks; it is recommended after 42 weeks and no later than 42 6/7 weeks.
