A healthy, 44-year-old woman, G2, P1, has a screening ultrasound at 18 weeks' gestation that shows no fetal anomalies. There is decreased fetal movement at 32 weeks' gestation, and ultrasound shows fetal growth restriction with relative sparing of the fetal head. The placenta appears normally positioned in the lateral fundus, but appears small, and the amniotic fluid index is reduced. Maternal blood pressure is normal. Which of the following conditions is most likely to be present?

The findings are typical for fetal growth restriction in later term, owing to relative sparing of the fetal brain. The findings suggest uteroplacental insufficiency from an intrinsic placental abnormality. One cause is a cytogenetic abnormality in the developing embryo that occurs just in the trophoblast, and only placenta is affected. Congenital syphilis occurs in the third trimester, when spirochetes can cross the placenta; there is typically placental and fetal hydrops. Inborn errors of metabolism such as galactosemia usually manifest after birth because maternal metabolism clears any intermediate products of fetal enzyme deficiencies. Preeclampsia is marked by maternal hypertension. An Rh incompatibility leads to fetal and placental hydrops. Trisomy 21 is more frequent with advancing maternal age, but in this case no fetal anomalies were noted.