<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><b>BACKGROUND: </b>Home visiting programs represent an important primary prevention strategy for adverse prenatal health behaviors; the various ways in which home visiting programs impact prenatal smoking cessation and reduction behaviors remain understudied.</p><p><b>METHODS: </b>Mixed methods approach using a retrospective cohort of propensity score matched home visiting clients and local-area comparison women with first births between 2008-2014 in a large Northeast state. Multivariable logistic and linear regression estimated third trimester prenatal tobacco smoking cessation and reduction. Additionally, qualitative interviews were conducted with 76 home visiting clients.</p><p><b>RESULTS: </b>A program effect was seen for smoking cessation such that clients who smoked less than ten cigarettes per day and those who smoked 20 or more cigarettes per day during the first trimester were more likely to achieve third trimester cessation than comparison women (p &lt;0.01 and p = 0.01, respectively). Only for heavy smokers (20 or more cigarettes during the first trimester) was there a significant reduction in number of cigarettes smoked by the third trimester versus comparison women (p = 0.01). Clients expressed the difficulty of cessation, but addressed several harm-reduction strategies including reducing smoking in the house and wearing a smoking jacket. Clients also described smoking education that empowered them to ask others to not smoke or adopt other harm reducing behaviors when around their children.</p><p><b>CONCLUSIONS: </b>While a significant impact on smoking cessation was seen, this study finds a less-clear impact on smoking reduction among women in home visiting programs. As home visiting programs continue to expand, it will be important to best identify effective ways to support tobacco-related harm reduction within vulnerable families.</p>