Factor VIII in pregnancy and birthweight.

Blood samples taken at 28 and 34 weeks of pregnancy from 495 women were assayed for factor VIII clotting activity (VIIIC) and factor VIII related antigen (VIIIR) to examine the distribution of these factors and to determine whether there was any relationship with birthweight. There was a small positive relationship of little clinical value between factor VIIIR and birthweight only when birthweight was adjusted for gestational age, sex of infant and parity. In pregnancies resulting in a male infant the level of factor VIIIC was lower at 34 weeks gestation than in pregnancies resulting in a female infant. A greater rise in the ratio of VIIIR/VIIIC was observed in women who had any type of hypertension when compared with normotensive pregnancies, but this was not associated with lower birthweight. Both factors VIIIR and VIIIC at 28 weeks gestation were lower for multiparous than for primiparous women, and were lower for those with eventual greater gestation at birth. Asian women had higher mean factor VIIIC than Caucasian women, a finding independent of the fact that women with blood group O had lower mean levels of factors VIIIR and VIIIC than women of other blood groups.