Women were recruited from the University of Washington Medical Center-associated obstetric units. Among the 2,577 women eligible for possible participation, 758 enrolled. Of these participants, 89 were not randomized. Among the 669 randomized women, 39 were not available for personal observation. These 39 were equally distributed among the three prophylaxis groups. In the final participant group, the infants of 630 women were evaluable.