TIMING OF INTRAPARTUM AMPICILLIN AND PREVENTION OF VERTICAL TRANSMISSION OF GROUP-B STREPTOCOCCUS

Objective: To evaluate the relationship between the time elapsed from the administration of ampicillin prophylaxis to delivery and its effic acy in interrupting intrapartum transmission of group B streptococcus. Methods: During the 12-month study period, all women who came to the Virgen de las Nieves Hospital (Granada, Spain) for delivery were scree ned for group B streptococcus vaginal carriage by a pigment-detection culture-based procedure. Colonized women were treated with ampicillin (2 g intravenously), and the interval between ampicillin administratio n and delivery was recorded. Newborns from colonized mothers also were screened to detect group B streptococcus colonization. Results: Durin g the study period, 4525 women were admitted to the hospital for deliv ery and screened for group B streptococcus vaginal colonization. Group B streptococcus was detected in 543 women (12%), of whom 454 gave bir th vaginally to 454 liveborn infants. Intrapartum ampicillin was given to 201 of these 454 women (44%), and 10% of the newborns from mothers who received intrapartum ampicillin prophylaxis were colonized by gro up B streptococcus. The relationship between timing of ampicillin admi nistration and rate of neonatal group B streptococcal transmission was as follows: less than 1 hour before delivery, 46%; 1-2 hours, 29%; 2- 4 hours, 2.9%; and more than 4 hours, 1.2%. Among the 253 mothers who received no intrapartum prophylaxis, colonization was found in 120 of their newborns (47%). Conclusion: When the time between the start of a mpicillin prophylaxis and delivery is at least 2 hours, vertical trans mission of group B streptococcus is minimized.