This study evaluated the magnitude, risk factors and outcomes of syphilis in pregnancy in a large cohort of women in four countries participating in the World Health Organization (WHO) antenatal care trial. All women attending the first prenatal care at each selected clinic were enrolled. Screening at the first antenatal visit was routinely performed with either rapid plasma reagin or Venereal Disease Research Laboratory and confirmed by fluorescent treponemal antibody absorption. All women also had the same syphilis tests after delivery. The initial prevalence, the incidence during pregnancy and the overall prevalence of syphilis at delivery were 0.9%, 0.4% and 1.3% respectively. Risk factors for syphilis during pregnancy were younger age for the incidence and older age and a history of stillbirth for the prevalence. Women with syphilis during pregnancy had significantly more adverse outcomes. We support the recommendation that in addition to the initial testing, a second routine test for syphilis ought to be established early in the third trimester even in low prevalence areas.