Triploid partial molar pregnancy detected through maternal serum alpha-fetoprotein and HCG screening.

BACKGROUND: Screening for Down syndrome using maternal serum alpha-fetoprotein (MSAFP) and hCG, with or without unconjugated estriol (E3), has become standard practice in much of the United States. When both MSAFP and hCG are elevated, the possibility of a partial molar pregnancy with fetal neural tube or abdominal-wall defect should be added to the differential diagnosis, as illustrated by this case.

CASE: A 22-year-old woman had elevated MSAFP and hCG levels on routine screening at 16 weeks' gestation. Ultrasound examination suggested a neural tube defect and a thickened placenta. Amniocentesis was performed. She very rapidly developed preeclampsia. Fluorescence in situ hybridization showed three distinct spots for the three probes tested. A triploid karyotype was confirmed with standard cytogenetic analysis. The fetus had an open neural tube defect, and placental pathology was consistent with a partial hydatidiform mole.

CONCLUSIONS: A possible partial molar pregnancy with abdominal-wall or open neural tube defect should be added to the differential diagnosis for interpreting Down syndrome screens when both MSAFP and hCG are elevated. A presumptive diagnosis of triploidy using fluorescence in situ hybridization was important in the management of this pregnancy.