Exposure to intrapartum antibiotic prophylaxis to reduce perinatal group B streptococcal disease was associated with increased childhood body mass index (BMI) persisting to age 10 years compared to no exposure (Δ BMI at 10 years: vaginal delivery 0.14 kg/m , caesarean 0.40 kg/m ).

<p><strong>OBJECTIVE: </strong>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).</p>

<p><strong>DESIGN: </strong>Retrospective cohort study of 13 804 infants.</p>

<p><strong>SETTING: </strong>Two perinatal centres and a primary paediatric care network in Philadelphia.</p>

<p><strong>PARTICIPANTS: </strong>Term infants born 2007-2012, followed longitudinally from birth to 5 years of age.</p>

<p><strong>EXPOSURES: </strong>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.</p>

<p><strong>OUTCOMES: </strong>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.</p>

<p><strong>RESULTS: </strong>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.</p>

<p><strong>CONCLUSION: </strong>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.</p>

<p><strong>BACKGROUND: </strong>Intrapartum antibiotic prophylaxis (IAP) reduce a newborn's risk of group B streptococcal infection (GBS) but may lead to an increased childhood body mass index (BMI).</p>

<p><strong>METHODS: </strong>Retrospective cohort study of infants (n=223,431) born 2007-2015 in an integrated healthcare system. For vaginal delivery, we compared children exposed to GBS-IAP and to any other type or duration of intrapartum antibiotics to no antibiotic exposure. For Cesarean delivery, we compared children exposed to GBS-IAP to those exposed to all other intrapartum antibiotics, including surgical prophylaxis. BMI over 5 years was compared using non-linear multivariate models with B-spline functions, stratified by delivery mode and adjusted for demographics, maternal factors, breastfeeding and childhood antibiotic exposure.</p>

<p><strong>RESULTS: </strong>In vaginal deliveries, GBS-IAP was associated with higher BMI from 0.5 to 5.0 years of age compared to no antibiotics (P&lt;0.0001 for all time points, Δ BMI at age 5 years 0.12&nbsp;kg/m 2, 95% CI 0.07 to 0.16&nbsp;kg/m 2). Other antibiotics were associated with higher BMI from 0.3 to 5.0 years of age. In Cesarean deliveries, GBS-IAP was associated with increased BMI from 0.7 years to 5.0 years of age (P&lt;0.05 for 0.7-0.8 years, P&lt;0.0001 for all other time points) compared to other antibiotics (Δ BMI at age 5 years 0.24&nbsp;kg/m 2, 95% CI 0.14 to 0.34&nbsp;kg/m 2). Breastfeeding did not modify these associations.</p>

<p><strong>CONCLUSION: </strong>GBS-IAP was associated with a small but sustained increase in BMI starting at very early age. This association highlights the need to better understand the effects of perinatal antibiotic exposure on childhood health.</p>