Prenatal Antibiotic Exposure Linked to Higher Group B Streptococcus Risk in Newborns: Study
A large population-based cohort study from Sweden has found that prenatal exposure to antibiotics was associated with an increased risk of group B Streptococcus (GBS) disease in newborns. Using data from four national registries covering all singleton live births in Sweden between 2006 and 2016, researchers from Karolinska Institutet reported these findings in the Journal of Infection, highlighting potential neonatal risks associated with antibiotic use during pregnancy. The study was published in the Journal of Infection by Thi Cam and colleagues.
Prenatal antibiotic exposure was found to be a risk factor for the incidence of Group B Streptococcus (GBS) infection in newborns during the first four weeks of life. GBS still tops the list of pathogens causing neonatal septicemia and meningitis. Although intrapartum antibiotic prophylaxis has effectively prevented early GBS infections among high-risk pregnancies, there is a lack of knowledge on the effect of antibiotic use during early pregnancy on GBS susceptibility in newborns and among pregnancies not meeting prophylaxis criteria.
In this population-based cohort study, all singleton live births in Sweden between 2006 and 2016 were included. Newborns were grouped depending on their exposure to systemic antibiotics during pregnancy. GBS colonization or disease was detected within the first four weeks of delivery. Multivariable logistic regression models employing robust variance estimation were applied to obtain adjusted odds ratios and their corresponding confidence intervals. The possibility of effect modification by known GBS risk factors was investigated.
Key findings
Out of 1,095,644 liveborn singletons, 24.5% had been exposed to antibiotics in utero. The rate of GBS infection in the neonate was also higher in exposed vs. unexposed neonates (0.86 vs. 0.66 per 1,000 live births).
Similarly, after adjustment, antibiotic exposure in utero was significantly related to a 29% increase in GBS infection (aOR, 1.29; 95% CI, 1.10-1.50).
Notably, the relationship remained robust in the absence of detected GBS risk factors, with an aOR of 1.34 (95% CI, 1.12-1.60) among neonates.
Conversely, in pregnancies with detected GBS risk factors, the associations were attenuated, indicating a differential impact depending on the need for GBS antibiotic prophylaxis.
Importantly, the timing since exposure mattered significantly as a variable.
Exposure in the early third trimester had the largest relationship with the risk of GBS infection in the neonate, increasing the risk by 67% (aOR, 1.67; 95% CI, 1.17-2.38).
Exposure to antibiotics in the last four weeks antecedent to delivery was initially shown to have a relationship with GBS infection risk, although the relationship was attenuated after the inclusion of all GBS infection risk factors, suggesting that the effect is partially confounded by indication.
Use of antibiotics prenatally increased the risk of neonatal GBS disease in the first four weeks post-delivery, and the early third trimester represented a period of particular susceptibility in the absence of known GBS risk factors in pregnancy. Findings of this study underscore the need for careful prenatal use of antibiotics and the need for further research in the optimization of preventive strategies for GBS disease in newborns.
Reference:
Ha, T. C. T., Orwa, S., Guedes, S., Moley, K., Wanneberger, K., Elfvin, A., Blaser, M. J., Gudnadottir, U., & Brusselaers, N. (2025). Antibiotic use during pregnancy and neonatal Group B Streptococcus disease. The Journal of Infection, 106669, 106669. https://doi.org/10.1016/j.jinf.2025.106669
