Antibiotic Prescribing for Group B Streptococcus Coverage in Preterm Prelabour Rupture of Membranes: A Retrospective Cohort Study

Background: Preterm prelabour rupture of membranes (PPROM) is the spontaneous rupture of fetal membranes prior to 37 weeks of pregnancy. Latency antibiotics, including macrolides with or without group B streptococcus (GBS)-covering antibiotics, are recommended as part of expectant management. Currently, there is no consensus on whether GBS-covering antibiotics should be prescribed. The primary objective of this retrospective cohort study was to characterize practice variation in GBS-covering antibiotic prescribing in PPROM. The secondary objective was to explore the association between maternal characteristics and GBS-covering antibiotic prescribing. Methods: Pregnant women with PPROM prescribed azithromycin (institutional standard antibiotic regimen) in 2024 and not in active labour were included. Maternal characteristics, stratified by GBS status, were compared. The association between antibiotic prescribing for GBS coverage and maternal factors was assessed using odds ratios. Two-sided p-values < 0.05 were considered statistically significant. Results: Out of the 181 admissions assessed for eligibility, 146 patients were included. Their GBS status at PPROM diagnosis was negative (19/146; 13%), positive (8/146; 5%), or unknown (119/146; 82%). The frequency of GBS-covering antibiotics prescribing was 5/8 (63%) in the positive group, 4/19 (21%) in the negative group, and 65/119 (55%) in those with an unknown GBS status. Aminopenicillin-based and penicillin regimens accounted for (69/74; 93%) of antibiotic regimens. Half (38/74; 51%) of the GBS-covering antibiotics were prescribed for 3–7 days, with a 33/74 (45%) completion rate as prescribed at PPROM diagnosis. The main reason for antibiotic discontinuation was negative GBS recto-vaginal swabs or urine cultures collected in those with an unknown GBS status at PPROM diagnosis, highlighting the role of microbiology laboratory testing in adjusting antibiotic therapy and facilitating antimicrobial stewardship. Aside from GBS status, no maternal characteristics were associated with GBS-covering antibiotic prescribing. Conclusions: At PPROM diagnosis, GBS coverage was prescribed in 21%, 63%, and 55% of patients with a negative, positive, and unknown GBS status, respectively. Only GBS status was associated with GBS-covering antibiotic prescribing. Further research is required to determine the impact of GBS coverage on perinatal outcomes.