Maternal and Microbiological Outcomes in GBS-Positive Patients Receiving Intrapartum Ampicillin versus Clindamycin: A Retrospective Cohort Study.

Abstract

Objectives: Early-onset Group B Streptococcus (GBS) infection is a major cause of neonatal morbidity and mortality, which can be prevented through intrapartum antibiotic prophylaxis (IAP). First-line β-lactams (penicillin or ampicillin) are preferred, whereas clindamycin is reserved for patients with a confirmed high-risk penicillin allergy and documented susceptibility. Increasing clindamycin resistance and concerns about intra-amniotic efficacy highlight the need to evaluate maternal outcomes. This study examined maternal infectious morbidity, neonatal outcomes, and microbiological findings in GBS-positive term patients receiving ampicillin versus clindamycin IAP.

Design: This retrospective cohort study was conducted between March 2021 and March 2024 at a tertiary university-affiliated hospital. Participants/Materials: Singleton term pregnancies (≥37 weeks) with a documented positive GBS vaginal-rectal culture obtained within 5 weeks before delivery were included. Patients received either ampicillin (n = 1,833) according to the institutional protocol or clindamycin (n = 78) if they reported a severe β-lactam allergy. No intrapartum clindamycin susceptibility testing was performed.

Setting: The study was conducted at a tertiary university-affiliated hospital between March 2021 and March 2024.

Methods: The co-primary outcomes were clinical chorioamnionitis and admission to the neonatal intensive care unit (NICU). Secondary maternal outcomes included intrapartum fever, postpartum fever, postpartum antibiotic administration use, and cesarean delivery. Secondary neonatal outcomes included a 5-min Apgar score of <7, umbilical cord pH at <7.1, respiratory distress, and ventilatory support. Chorioamniotic swabs were obtained after delivery. Data were analyzed using chi-square or Fisher's exact tests for categorical variables, t tests or Mann-Whitney U tests for continuous variables, and multivariable logistic regression to identify independent predictors.

Results: Baseline maternal and obstetric characteristics were similar. Compared with ampicillin, clindamycin was associated with significantly higher rates of intrapartum fever (23.1% vs. 2.3%, p < 0.001), clinical chorioamnionitis (9.0% vs. 0.5%, p < 0.001), postpartum fever (5.1% vs. 1.0%, p = 0.001), and postpartum antibiotic use (7.6% vs. 0.8%, p < 0.001). Cesarean delivery rates did not differ significantly (19.2% vs. 11.6%, p = 0.084). NICU admission and other neonatal outcomes were comparable. Compared with ampicillin, clindamycin IAP was identified as a strong independent predictor of clinical chorioamnionitis (adjusted odds ratio [aOR] 20.1, 95% confidence interval [CI] 6.6-61.4, p < 0.001), together with prolonged rupture of membranes >18 h (aOR 4.9, 95% CI 1.6-15.7, p = 0.006) and cervical ripening by catheter balloon (aOR 4.1, 95% CI 1.2-13.6, p = 0.023). Postpartum, GBS-positive chorioamniotic cultures were significantly more frequent among patients who received clindamycin compared with those who received ampicillin (28.2% vs. 10.5%; p < 0.001).

Limitations: This retrospective, single-center study may be subject to bias and has limited generalizability. The small clindamycin group reduced the power for rare outcomes. Penicillin allergy was self-reported without confirmatory testing, and clindamycin susceptibility was not assessed intrapartum.

Conclusions: Among GBS-positive term patients, intrapartum clindamycin prophylaxis was associated with markedly higher maternal infectious morbidity and increased GBS detection in chorioamniotic cultures compared with ampicillin, without significant differences in neonatal outcomes. These findings raise concerns about the intra-amniotic effectiveness of clindamycin and support minimizing its use whenever possible. Further prospective studies are warranted to confirm these findings and to evaluate alternative prophylactic regimens for patients with penicillin allergy.

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