Maternal body mass index and the risk of early-onset Group B Streptococcus disease in newborns: A systematic review and meta-analysis
Clinical Snapshot
PICO Framework
| P — Population | Pregnant women and their newborns from 19 observational studies (n=3,707,047 women, 277,887 cases) |
| I — Intervention | High prepregnancy body mass index (BMI) |
| C — Comparator | Normal BMI (reference BMI 22.3) |
| O — Outcomes | Early-onset group B Streptococcus disease (EOGBS) and proxy outcomes including intrapartum vaginal GBS colonization and rectovaginal/urinary GBS colonization |
Bottom Line
This systematic review of 19 studies encompassing 3.7 million women demonstrates a modest but statistically significant association between increasing maternal BMI and early-onset Group B Streptococcus disease risk. For every unit increase in BMI, the odds increase by 2.4%, translating to a 40% increased risk at BMI 35 and 70% increased risk at BMI 45 compared to normal BMI. While the overall association is modest, the large effect size in severely obese women (BMI >35) suggests clinical relevance. The findings support incorporating BMI into existing GBS risk assessment protocols, particularly in the Australian context where universal screening is standard practice. However, the evidence quality is limited by reliance on observational data and lack of formal GRADE assessment. Clinicians should consider elevated BMI as an additional risk factor when counselling patients about GBS prophylaxis, while recognising that current screening and prophylaxis protocols remain the primary prevention strategy.
Key Findings
P Value: Not explicitly reported
Effect Size: OR 1.4 for BMI 35 vs normal BMI; OR 1.7 for BMI 45 vs normal BMI
Primary Outcome: 2.4% increase in odds ratio per unit BMI increase for EOGBS and proxy outcomes
Nnt Or Sensitivity: Large study subset: HR 2.4 (95% CI 1.7-3.4) for BMI 35.0-39.9 vs normal BMI
Confidence Interval: BMI 35: OR 1.4 (95% CI 1.1-1.6); BMI 45: OR 1.7 (95% CI 1.3-2.3)
Clinical Application
BMI is routinely measured in Australian antenatal care, making this risk factor easily assessable Relevant to Australian practice where RANZCOG guidelines recommend universal GBS screening at 35-37 weeks. May inform risk stratification protocols and antibiotic prophylaxis decisions in high-BMI pregnancies Pregnant women undergoing routine antenatal care, particularly those with elevated BMI requiring GBS risk stratification
Abstract
BACKGROUND: Early-onset group B Streptococcus disease (EOGBS) remains a leading cause of neonatal morbidity and mortality. The incidence can be substantially reduced by intrapartum antibiotic prophylaxis in women with defined risk factors. However, the role of high prepregnancy body mass index (BMI) as a risk factor remains unclear. This systematic review and meta-analysis therefore aimed to evaluate the association between maternal BMI and the risk of EOGBS, as well as related proxy outcomes, including intrapartum vaginal GBS colonization and rectovaginal or urinary GBS colonization before term. METHODS: We systematically searched MEDLINE, Embase, and Cochrane CENTRAL on the 28th of January 2026, for studies examining the relationship between pregestational BMI and EOGBS or its proxy outcomes. Eligible studies included observational and interventional designs but not case reports and conference abstracts. Risk of bias was assessed using the QUIPS tool. Random-effects meta-regression and sensitivity analyses were performed. RESULTS: We identified 19 eligible observational studies reporting data from a total of 3,707,047 women, encompassing 277,887 cases. For the risk of EOGBS and its proxy outcomes, assuming a log-linear association, our meta-regression showed a 2.4% increase in the odds ratio (OR) per unit increase in BMI. This corresponds to an OR of 1.4 (95% CI 1.1-1.6) for a BMI of 35 and 1.7 (95% CI 1.3-2.3) for a BMI of 45, compared to a normal BMI of 22.3. One very large study on 1,971,346 live singleton births with 780 EOGBS cases, found a hazard ratio of 2.4 (95% CI 1.7-3.4) for a BMI of 35.0-39.9 compared to normal BMI (18.5-24.9). CONCLUSIONS: Although the overall association appears modest, incorporating BMI may improve prevention strategies for EOGBS .
References
- 1.Graae, E. E., Uldbjerg, N., Skjøth, F., Bech, M. A., Nielsen, P. N., Karkov, S. R., Moos, C. M., & Khalil, M. R. (2026). Maternal body mass index and the risk of early-onset Group B Streptococcus disease in newborns: A systematic review and meta-analysis. PLoS One. https://doi.org/10.1111/1471-0528.15871
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