Our aim was to determine the prevalence and sequelae of positive acquired thrombophilia serology in the asymptomatic low-risk primigravid population. We undertook a prospective blinded study of 1011 primigravid patients screening for lupus anticoagulant, anticardiolipin antibody, anti-beta(2) glycoprotein-1 and antinuclear antibody assessment at booking and 36 weeks gestation. Serial ultrasounds of the fetus with uterine and umbilical Dopplers and placental evaluation were performed at 24 and 36 weeks gestation. Antenatal course, labour and delivery outcome and placental histology were reviewed. The incidence of positive acquired thrombophilia serology was 27.4%. Overall, there was no difference in rates of fetal loss or maternal disease between women with positive acquired thrombophilia serology and the control population. Routine testing for acquired thrombophilic traits is therefore not warranted.