Evaluation of maternal serum dimeric inhibin A as a first-trimester marker of Down's syndrome.

While second-trimester prenatal screening programmes for Down's syndrome have become established in prenatal care, it would be advantageous to be able to offer screening in earlier pregnancy. To this end, we have evaluated a new potential maternal serum marker, dimeric inhibin A, as a possible first-trimester marker. Dimeric inhibin A was measured in prospectively collected maternal serum from 23 cases of Down's syndrome and matched chromosomally normal controls, at 11-13 weeks' gestation. Levels of this protein were significantly elevated in the Down's pregnancies compared with the control pregnancies. The median multiple of the normal median (MOM) for the Down's samples was 2.46 (95 per cent confidence interval: 2.11-3.26, P < 0.0001 vs. controls). These results suggest that dimeric inhibin A is a useful discriminator of Down's-affected pregnancies from normal pregnancies in the first trimester and that sensitive screening in combination with maternal age and other possible markers may be practicable in the first trimester.