Inhibin A is a maternal serum marker for Down's syndrome early in the first trimester

Inhibin A is a maternal serum marker for fetal Down's syndrome (DS) in the second trimester. We examined whether inhibin A could be used early in the first trimester. Maternal serum concentrations of inhibin A were determined in 81 controls and 27 cases of fetal trisomy 21 in gestational week 5-11. The log MoM (Multiple of the Median of normal pregnancies) inhibin A concentration in DS pregnancies increased with gestational age (p = 0.001) from a mean log MoM (standard deviation) of -0.1754 (0.3712) (n = 11) in week 7-8 to a mean log MoM (standard deviation) of 0.1842 (0.2145) (n = 12) in week 9-11. This corresponded to an increase in inhibin median MoM from 0.67 to 1.53. When inhibin A was used together with pregnancy-associated plasma protein-A, free beta-human chorionic gonadotrophin and nuchal translucency as DS markers, the estimated detection rates were 81.4 and 82.6% in weeks 7-8 and 9-11, respectively, for false-positive rates of 0.9 and 1.0%. The performance of the latter combination early in the first trimester is nearly as good as that of integrated first- and second-trimester screening, with the further advantage that the risk can be reported to the pregnant woman in first trimester.