Combined ultrasonography and amniocentesis for pregnant women with elevated serum alpha-fetoprotein. Revising the risk estimate.

A combination of ultrasound and amniocentesis for alpha-fetoprotein (AFP) and acetylcholinesterase (ACHE) identified 36 anomalous fetuses among 331 pregnant women evaluated at our center for "true" elevated maternal serum alpha-fetoprotein (MSAFP). In six cases the diagnosis of fetal anomalies was missed on initial ultrasonography. In addition, placental pathology was identified in 12 cases and adverse outcome (fetal demise, intrauterine growth retardation, severe oligohydramnios) in 15. When grouped by multiples of the median (MOM), a significant linear correlation was observed between increasing MSAFP and the rate of fetal anomalies or adverse outcome. The frequency of fetal anomalies increased from 0.93% when MSAFP was less than 3.0 MOM to 56% when MSAFP was greater than 7.5 MOM. No differences were observed in the frequency of placental pathology between the groups. A normal ultrasound study in these patients will decrease considerably, but not eliminate, the risk estimate for undetected fetal anomalies. From our 83% ultrasound sensitivity we calculate that with MSAFP greater than 3.0 MOM the risk of anomalies despite a reassuring scan is greater than 1% and clearly warrants offering amniocentesis for amniotic fluid AFP and ACHE. Between 2.5 and 3.0 MOM the risk is relatively low. Amniocentesis should be offered routinely to patients with MSAFP greater than 3.0 MOM and normal ultrasonography. In patients with MSAFP of 2.5-2.9 MOM and satisfactory ultrasonography the risk of amniocentesis may outweigh its benefits.