Plasma assay of fetal factors VIIIC and IX for prenatal diagnosis of haemophilia.

Fetal blood unmixed with maternal blood or amniotic fluid was obtained by direct-vision fetoscopy in 22 consecutive cases at 15--22 weeks' gestation; the investigation was done either for prenatal diagnosis or before therapeutic abortion. Fetal plasma factors VIIIC and IX averaged 50 I.U./dl (S.D. 12.8) and 12.5 I.U./dl (S.D. 2.4), respectively. Two male fetuses at risk of haemophilia had normal factor VIIIC levels by these criteria, and both pregnancies ended in the birth of a normal boy. Five others gave 3 normal and 2 haemophilic results, which were confirmed in two of the three terminated pregnancies.