Prenatal Group B Streptococcal colonization and caesarean scar niche after first caesarean section: an ambidirectional cohort study

A caesarean scar niche, particularly a large niche, is associated with important long-term gynaecological and reproductive complications. Although the neonatal consequences of prenatal Group B Streptococcus (GBS) colonization are well recognized, its association with maternal scar healing after caesarean section (CS) has received limited attention. To investigate whether prenatal GBS colonization is associated with caesarean scar niche and postmenstrual spotting after a first CS. This ambidirectional cohort study included 152 women (74 GBS-positive and 78 GBS-negative) who underwent their first CS at the first affiliated hospital of Anhui Medical University, China between January 2022 and April 2024. GBS status and delivery-related covariates were obtained retrospectively from medical records. Questionnaires and research-specific transvaginal ultrasonography (TVS) were completed prospectively at a follow-up visit conducted at least 12 months after CS. GBS colonization was assessed before CS by direct latex agglutination. Niche dimensions, residual myometrial thickness (RMT), adjacent myometrial thickness (AMT), and depth/AMT ratio were assessed by TVS; postmenstrual spotting was self-reported. Compared with GBS-negative women, GBS-positive women had higher adjusted odds of postmenstrual spotting (adjusted odds ratio [aOR]: 9.78, 95% confidence interval [CI]: 3.50 ~ 27.35), small niche (aOR:5.39, 95% CI: 1.57 ~ 18.45), and large niche (aOR: 6.55, 95% CI: 2.52 ~ 17.06). Among women with a niche, prenatal GBS colonization were also associated with lower RMT (adjusted β:-0.56, 95% CI: -0.97~-0.15). In this observational study, prenatal GBS colonization was associated with higher odds of postmenstrual spotting and caesarean scar niche after a first CS. These hypothesis-generating findings warrant validation in larger prospective studies with standardized follow-up and microbiological assessment to clarify the association and its potential clinical implications.