The cesarean delivery rate in the United States has increased from 5% in 1970 to around 32% in recent years and has plateaued, despite attempts at reduction. Labor is an inflammatory process, but excessive inflammation (for example, related to infection or the meta-inflammatory state associated with obesity) is detrimental to the normal labor process. Dysfunctional labor is a major cause of cesarean delivery. A pilot randomized clinical trial found that patients treated with a prophylactic antibiotic regimen (cefazolin and azithromycin) during labor induction had a lower rate of cesarean delivery than those receiving placebo. Cesarean delivery rates were 41.1% and 26.8%, respectively. A subset of the cohort also received intrapartum antibiotics aimed at group B streptococcus (IAP for GBS) in parallel to the study if they tested positive for the bacteria during their prenatal care to prevent GBS sepsis of the neonate. In a planned secondary analysis of this subset of GBS positive patients, we did not observe a decrease in the cesarean delivery rate when comparing those that received the study regimen with the group that received placebo.

We hypothesize that IAP for GBS alone may also reduce the cesarean rate, potentially by decreasing subclinical and clinical infection and therefore reducing excessive inflammation, which can contribute to abnormal labor.

We conducted a retrospective cohort study of nulliparous women who delivered at our institution. We included patients who underwent an induction of labor (IOL) in 2020-2022 which were induced at or beyond 37 weeks of gestation, with singleton gestations and between the ages 15-49 years of age. Multifetal gestations, multiparous patients, and fetuses with major anomalies were excluded. We aimed to compare the cesarean delivery rate between those treated with intrapartum GBS prophylaxis and those who did not receive any intrapartum antibiotics. Our primary outcome was cesarean delivery rate between the two cohorts. Secondary outcomes examined associated maternal and neonatal morbidity. 

There were 1182 patients who underwent induction of labor and met inclusion criteria. There were 941 patients who did not receive GBS prophylaxis and 244 who did. The cesarean delivery rate was additionally similar between the two groups with a rate of 25.7% for those who did not receive GBS prophylaxis and 27.9% in those who did (p=0.50). Adjusted RR for cesarean delivery was 0.95 (0.76, 1.18; 95% CI). Additionally, a composite of maternal outcomes was no different between the two cohorts. NICU admission rates and a composite of neonatal outcomes were noted to be lower in the subset of patients receiving GBS prophylaxis with adjusted RR 0.51 (0.28, 0.93; 95% CI) 

Our study does not support a reduction in cesarean delivery rate attributable to GBS prophylaxis alone. Given results of prior studies, additional studies should be performed to assess for a reduction in rate of cesarean delivery with broad-spectrum antibiotics such as cefazolin and azithromycin in labor.