OBJECTIVE: To compare ampicillin with and without sulbactam with respect to the effect on the latency period after preterm premature rupture of membranes (PROM). METHODS: Patients with PROM at 25-35 weeks' gestation were offered participation in a randomized blinded trial comparing ampicillin-sulbactam with ampicillin. Evaluations for cervical pathogens were performed on admission and patients were followed-up with daily maternal and fetal evaluation. Maternal and neonatal outcomes were analyzed using indicated techniques. RESULTS: Fifty-three women were studied, with 25 receiving ampicillin-sulbactam and 28 receiving ampicillin. The ampicillin-sulbactam group had a significantly longer latency period (433 +/- 625 versus 143 +/- 165 hours, P = .03) and significantly fewer neonatal complications (five versus 20, P