Intrapartum group B Streptococcal prophylaxis and childhood weight gain.

Objective: To determine the difference in rate of weight gain from birth to 5 years based on exposure to maternal group B streptococcal (GBS) intrapartum antibiotic prophylaxis (IAP).

Design: Retrospective cohort study of 13 804 infants.

Setting: Two perinatal centres and a primary paediatric care network in Philadelphia.

Participants: Term infants born 2007-2012, followed longitudinally from birth to 5 years of age.

Exposures: GBS IAP defined as penicillin, ampicillin, cefazolin, clindamycin or vancomycin administered ≥4 hours prior to delivery to the mother. Reference infants were defined as born to mothers without (vaginal delivery) or with other (caesarean delivery) intrapartum antibiotic exposure.

Outcomes: Difference in rate of weight change from birth to 5 years was assessed using longitudinal rate regression. Analysis was a priori stratified by delivery mode and adjusted for relevant covariates.

Results: GBS IAP was administered to mothers of 2444/13 804 (17.7%) children. GBS IAP-exposed children had a significantly elevated rate of weight gain in the first 5 years among vaginally-born (adjusted rate difference 1.44% (95% CI 0.3% to 2.6%)) and caesarean-born (3.52% (95% CI 1.9% to 5.2%)) children. At 5 years, the rate differences equated to an additional 0.24 kg among vaginally-born children and 0.60 kg among caesarean-born children.

Conclusion: GBS-specific IAP was associated with a modest increase in rate of early childhood weight gain. GBS IAP is an effective intervention to prevent perinatal GBS disease-associated morbidity and mortality. However, these findings highlight the need to better understand effects of intrapartum antibiotic exposure on childhood growth and support efforts to develop alternate prevention strategies.