1305 FIRST TRIMESTER MATERNAL SERUM ALPHA-FETOPROTEIN (MSAFp) SCREENING

Abstract

Second trimester MSAFP screening is valuable in the prenatal detection of neural tube defects and in the recognition of other problems. Our screening leads to amniocentesis in 1:400, but not infrequently leads to a later conclusion of prenatal studies with options to abort often between 20-24 wks. DB has established an extremely sensitive “simultaneous-sandwich” radioimmunoassay (M-RIA) with polystyrene beads coated with anti-AFP monoclonal antibodies and using solid phase support. Comparative assays to available polyvalent commercial kits showed M-RIA to be 4-10 times more sensitive. In addition, inter- and intra-assay variation and reproducibility were assessed over a wide range of values. Results were noted to be accurate with a coefficient of variation < 5%. MRIA studies of 400 non-pregnant females showed serum AFP undetectable in 99.6%, others having MSAFP values < 3 ng/ml. We have analysed 449 first trimester MSAFP samples, from apparently normal pregnancies. We report that AFP was detectable between 8-9 wks, significant (p <0.001)AFP “elevations” were noted at 10 wks, AFP rose linearly 10-24 wks, SEM's were small, higher AFP levels were found & M-RIA was accurate, precise, & reproducible. 3/4 patients have also had a 2nd trimester MSAFP screen. Correlations between ultrasound studied pregnancies, 1st and 2nd trimester AFPs, and outcome will be presented. These preliminary data suggest that MSAFP screening may be possible earlier than 16 wks and even in the 1st trimester.