Maternal serum pregnancy-associated plasma protein A (PAPP-A) but not pregnancy-specific beta 1-glycoprotein (SP1) is a useful second-trimester marker for fetal trisomy 18

The usefulness of early second-trimester serum determinations of pregnancy- associated plasma protein A (PAPP-A) and pregnancy-specific beta 1-glycopro tein (SP1) in suspected cases of fetal trisomy 18 was examined in a retrosp ective, cross-sectional study. Maternal serum PAPP-A and SP1 in 20 cases of fetal trisomy 18 between 15 and 20 weeks of pregnancy, and in 40 controls matched for gestational age and storage time were determined and compared w ith hCG and free oestriol (uE(3)). In trisomy 18, the reduction in serum co ncentration was found to be more pronounced for PAPP-A than for hCG and fre e oestriol. While none of the 40 control sera had a MoM below 0.2 for eithe r PAPP-A, hCG or uE(3), in the trisomy 18 group (20 cases) 17 (85 per cent) of the PAPP-A but only 5 (25 per cent) of the hCG and 4 (20 per cent) of t he uE(3) results were below the 0.2 MoM threshold. SP1 did not distinguish between controls and trisomy is. This chromosomal abnormality is too rare a condition to justify maternal serum PAPP-A determination in the second tri mester as a routine procedure, but such a test can play a useful role whene ver the risk of trisomy 18 is found to be only marginally increased after h CG and uE(3) measurements. Copyright (C) 1999 John Wiley & Sons, Ltd.