A 32-year-old woman, gravida 3 para 2, at 41 weeks gestation comes to the office for a routine prenatal visit. She has had no contractions, vaginal bleeding, or leakage of fluid. Fetal movement is normal. The patient's pregnancy has been uncomplicated. An ultrasound at 18 weeks gestation showed normal fetal anatomy and a posterior placenta. She has no chronic medical conditions and has had no previous surgeries. Her other pregnancies ended in vaginal deliveries at term. The patient takes a daily prenatal vitamin and does not use tobacco, alcohol, or illicit drugs. Blood pressure is 110/80 mm Hg and pulse is 80/min. BMI is 28 kg/m². Fundal height is 40 cm. The cervix is 1 cm dilated and 10% effaced. Nonstress test is reactive. The patient would like to await spontaneous labor rather than undergo an induction. Delaying delivery to 42 weeks gestation in this patient increases the risk of which of the following pregnancy-related complications?

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11ec25c8_da75_c1f7_bc81_c38b90323099_MD0003_00 This patient has a late-term pregnancy, defined as ≥41 weeks gestation. Late- and post-term (≥42 weeks gestation) pregnancies are at risk of decreased placental function due to age-related placental changes (eg, infarctions, calcifications) that cause increased placental vascular resistance. Progressive placental dysfunction can lead to uteroplacental insufficiency and chronic fetal hypoxemia, which cause central nervous system suppression and intrauterine fetal demise. To prevent this suppression, blood is preferentially distributed to the brain rather than peripheral tissue. This redistribution can be evidenced on ultrasound as oligohydramnios (single deepest pocket <2 cm or amniotic fluid index <5 cm) as amniotic fluid is dependent on renal perfusion and urine production. Because the risk of uteroplacental insufficiency increases with gestational age, patients with late- and post-term pregnancies require frequent fetal monitoring (eg, nonstress test, ultrasound for amniotic fluid volume). Patients with findings suggestive of uteroplacental insufficiency, such as late decelerations or oligohydramnios, require delivery to prevent intrauterine fetal demise. (Choice A) Risk factors for abruptio placentae include hypertension, cocaine use, abdominal trauma, and a prior abruptio placentae. It is not associated with post-term pregnancy. (Choice B) Late- and post-term pregnancies are at risk for fetal macrosomia (weight ≥4.5 kg [9.9 lb]) and severe maternal obstetric lacerations. In contrast, low fetal birth weight (<2.5 kg [5.5 lb]) typically occurs in preterm infants. (Choice D) Risk factors for placenta accreta include prior cesarean delivery (particularly in patients with a placenta previa in the current pregnancy) and prior uterine myomectomy. (Choice E) Polyhydramnios (single deepest pocket ≥8 cm or an amniotic fluid index of ≥24 cm) is associated with congenital fetal malformations (eg, esophageal atresia, anencephaly) and maternal diabetes mellitus. (Choice F) Risk factors for preeclampsia include extremes of maternal age (eg, <18, >40), nulliparity, chronic hypertension, diabetes mellitus, and renal disease. Educational objective: Patients with late-term (≥41 weeks gestation) and post-term (≥42 weeks gestation) pregnancies are at increased risk for oligohydramnios, a marker for placental insufficiency and an indication for delivery. They are therefore routinely evaluated for this and other markers of placental insufficiency (eg, late decelerations). References: Practice bulletin no. 146: management of late-term and postterm pregnancies. (http://www.ncbi.nlm.nih.gov/pubmed/25050770) Postterm pregnancy. (http://www.ncbi.nlm.nih.gov/pubmed/24753906)

A 32-Year-Old Woman, Gravida 3 Para 2, at 41 Weeks