A 32-year-old G3P20L2 presents to the obstetrician's office for a routine OB visit at 30 weeks. She has had no complications during the pregnancy and has had regular prenatal care. Her gestational age is confirmed with a first-trimester sonogram. During the routine OB visit, the fundal height measures 35 cm. All of the following can explain the size-date discrepancy except

(Gabbe, 2/e, p 230.) Uterine fibroids, polyhydram- nios (excessive amniotic fluid), fetal macrosomia, and twin gestation are all plausible explanations of why the uterine size would measure larger than expected for the patient's dates. It is unlikely, but possible, that a twin gestation would have been missed with an early sonogram. The fundal height in centimeters has been found to correlate with gestational age in weeks with an error of 3 cm from 16 to 38 weeks.