DUAL POSITIVITY FOR NEURAL-TUBE DEFECTS AND DOWN-SYNDROME AT MATERNALSERUM SCREENING - GESTATIONAL OUTCOME

Objective: To evaluate the gestational outcome of pregnancies screen-p ositive for both neural tube defects (NTD) and Down syndrome (DS) ('du al positivity'). Methods: Among 10,667 mid-trimester women screened fo r DS and NTD with alpha-fetoprotein (AFP), unconjugated estriol (uE(3) ), and human chorionic gonadotropin (hCG), delivered up to July 1996, we have selected cases with both an unexplained AFP value greater than or equal to 2.5 multiples of median (MoM) and a DS risk greater than or equal to 1:250. All these pregnant women were managed with amniocen tesis and/or CVS, ultrasound scans, and Doppler velocimetry. We have c ollected all data about the gestations with 'dual positivity' and no o bvious explanation for these findings (cases with fetal malformations related to raised AFP). Results: Twelve women (1.1:1,000) showed unexp lained 'dual positivity'. Abnormal karyotypes were found in 3 fetuses, and pregnancies were terminated: there were 2 triploidies with partia l hydatiform mola, and 1 DS. In 9 cases the fetal karyotype was normal , but a confined placental trisomy 16 was found in 4. Of the 9 continu ing gestations, 8 displayed fetal growth retardation (FGR). One gestat ion ended with fetal death at 27 weeks. All 9 fetuses were morphologic ally normal, and 8 were small for gestational age. Conclusions: 'Dual positivity' at NTD/DS screening may anticipate pregnancy complications . The finding of trisomy 16 confined to the placenta and FGR in 4 case s suggests that at least some fetuses with growth restriction may suff er from a distinct placental disease. Maternal serum screening may hav e implications different from DS and NTD, as demonstrated by the 2 cas es with triploidy and incomplete hydatiform mola, the 4 cases with pla cental trisomy 16, and the 4 cases of FGR of the 5 fetuses without chr omosome abnormalities. As the pathologic outcome of these pregnancies is more important than the mere serum screening results, we feel that these cases need a strict work-up, including CVS, amniocentesis and ul trasound studies to better address the obstetrical management.