MATERNAL SERUM INHIBIN-A AND FREE BETA-HCG CONCENTRATIONS IN TRISOMY-21 PREGNANCIES AT 10 TO 14 WEEKS OF GESTATION

Objective To determine the relation between maternal serum inhibin-A a nd free beta-hCG concentrations in chromosomally normal pregnancies an d to compare the two biochemical markers for their sensitivity in iden tifying trisomy 21 pregnancies. Sample Inhibin-A and free beta-hCG wer e measured in maternal serum samples from 800 chromosomally normal sin gleton pregnancies at 10 to 14 weeks of gestation and 76 singleton pre gnancies with fetal trisomy 21. Results In the normal group maternal s erum inhibin-A was significantly associated with both maternal weight and gestational age (F = 11.2, P < 0.0001). In pregnancies with trisom y 21 the maternal serum inhibin-A and free beta-hCG concentrations wer e significantly increased (mean difference inhibin = 0.51 SD, F = 18, P < 0.0001 and mean difference free beta-hCG = 1.13 SD, F = 80, P < 0. 0001). For a 5% false positive rate, the sensitivity of maternal serum free beta-hCG in identifying pregnancies with trisomy 21 was 28.9% co mpared with 12.8% for maternal serum inhibin-A. Delta inhibin-A was si gnificantly associated with delta-free beta-hCG (r = 0.345, P < 0.01) and the deviation from the normal mean for free beta-hCG was significa ntly greater than the deviation for inhibin-A (t = 4.0, P < 0.0001). F or a 5% false positive rate, the sensitivity achieved by combining inf ormation from delta inhibin-A and delta free beta-hCG was similar to t he sensitivity of free beta-hCG alone (30.3% compared with 28.9%) Conc lusion At 10 to 14 weeks of gestation fetal trisomy 21 is associated w ith increased maternal serum inhibin-A and free beta-hCG levels. Howev er, the degree of elevation of inhibin-A is less than that of free bet a-hCG, and there is a significant association between levels of the tw o proteins. The sensitivity for trisomy 21 achieved with the combinati on of maternal serum inhibin-A and free beta-hCG is not significantly different from that achieved with maternal serum free beta-hCG alone.