MATERNAL SERUM INHIBIN-A LEVELS IN TWIN PREGNANCIES - IMPLICATIONS FOR SCREENING FOR DOWNS-SYNDROME

A nested case-control study using stored serum samples collected as pa rt of a prospective study of the outcome of pregnancy was performed to investigate concentrations of (dimeric) inhibin-A in maternal serum b etween 15 and 22 weeks of pregnancy in 200 twin pregnancies and 600 si ngleton control pregnancies. Each twin pregnancy was matched with thre e singleton pregnancies for gestational age (same completed week) and duration of sample storage (same calendar year), although for one twin there was insufficient serum. The median inhibin-A level in the twin pregnancies was 1.99 multiples of the median (MOM) for singleton pregn ancies (P<0.001) [95 per cent confidence interval (CI) 1.83-2.16]. The se results enable inhibin-A values to be adjusted so that prenatal scr eening for Down's syndrome can be performed using this marker in twin pregnancies as well as in singleton pregnancies.