Serum müllerian-inhibiting substance in Down's syndrome pregnancies.

BACKGROUND To examine whether maternal serum levels of müllerian-inhibiting substance (MIS) differ in Down's syndrome and unaffected pregnancies. METHODS Case-control study was conducted using stored serum from an antenatal screening programme. Sera from 25 Down's syndrome pregnancies were retrieved from -20 degrees C storage together with 125 unaffected controls individually matched for maternal age, weeks of gestation and duration of storage. Results were expressed in multiples of the gestation-specific median value (MoM) in controls. RESULTS The median value in Down's syndrome pregnancies was 0.83 MoM (P = 0.77, two-tail Wilcoxon rank sum test). Among unaffected pregnancies, there was a statistically significant correlation between MIS and pregnancy-associated plasma protein-A (P < 0.05). MIS levels were elevated in pregnancies where assisted reproduction techniques had been used. CONCLUSION There is no evidence for a substantial reduction in maternal serum MIS levels in Down's syndrome pregnancies. This study provides useful information regarding serum MIS levels in pregnancy.