Maternal serum inhibin-A levels in twin pregnancies: implications for screening for Down's syndrome

A nested case-control study using stored serum samples collected as part of a prospective study of the outcome of pregnancy was performed to investigate concentrations of (dimeric) inhibin-A in maternal serum between 15 and 22 weeks of pregnancy in 200 twin pregnancies and 600 singleton control pregnancies. Each twin pregnancy was matched with three 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 pregnancies (P < 0.001) [95 per cent confidence interval (CI) 1.83-2.16]. These results enable inhibin-A values to be adjusted so that prenatal screening for Down's syndrome can be performed using this marker in twin pregnancies as well as in singleton pregnancies.