2ND-TRIMESTER SCREENING FOR DOWNS-SYNDROME USING MATERNAL SERUM DIMERIC INHIBIN-A

BACKGROUND AND OBJECTIVE Prenatal maternal serum screening for Down's syndrome has become an important and established part of modern antena tal care. Previously it has been reported that non-specific immunoreac tive inhibin may be useful in this context. Using a novel assay we hav e evaluated dimeric inhibin A as a possible second trimester marker of Down's syndrome. METHODS From 1992-1993 records, stared sera from wom en with Down's affected pregnancies and chromosomally normal control p regnancies were identified and retrieved for analysis. These sera had been prospectively collected at 15, 16 and 17 weeks gestation. SUBJECT S Records revealed 21 women who had had a Down's syndrome pregnancy an d who also had serum available for analysis. Sera from 150 chromosomal ly normal controls, matched for gestation and duration of storage, wer e also retrieved.MEASUREMENTS Dimeric inhibin A was measured using a r ecently developed two-site enzyme-linked immunoassay. This employs a c apture anti inhibin beta(A)-subunit monoclonal antibody, covalently bo und to a microtitre plate and a second anti inhibin alpha-subunit anti body conjugated to alkaline phosphatase, allowing detection. RESULTS T he mean (95% CI) maternal serum dimeric inhibin A in the samples from control pregnancies was 237 (201.5-273.4) ng/l, 266.9 (235.4-298.5) ng /l and 207.2 (178.5-235.9) ng/l at 15, 16 and 17 weeks gestation respe ctively. Expressing the results from the Down's samples as multiples o f the normal median (MoM), the median (95% CI) MoM was 2.6 (2.25-3.57) , significantly higher than the controls (P < 0.0001, Mann-Whitney U-t est). In the sample set tested, for a given false positive rate of 5.3 % inhibin A alone afforded a detection rate of 62%, detecting cases pr eviously undetected by routine screening. CONCLUSIONS Dimeric inhibin A appears to be a promising new marker for the prenatal detection of D own's syndrome. Further prospective evaluation and assessment with oth er established markers would now be merited.