The impact of Vaginal Flora Screening in the third trimester on pregnancy outcomes in primiparas undergoing vaginal delivery: a retrospective cohort study

BACKGROUND: The necessity of third-trimester vaginal flora screening remains debated. This study aims to evaluate the association between third-trimester vaginal flora screening and pregnancy outcomes among primiparous women undergoing vaginal delivery, as well as neonatal health outcomes. METHODS: This study enrolled 1,380 primiparous women with singleton pregnancies who underwent GBS screening alone or combined GBS plus vaginal flora screening at 35-37 weeks of gestation. Participants were categorized into two cohorts: Group A (GBS screening only; n = 880) and Group B (GBS plus vaginal flora screening; n = 500). Group B was further stratified into Group C (vaginal flora-negative; n = 229) and Group D (vaginal flora-positive; n = 271). After excluding 40 women with positive GBS results from Group D, the remaining 231 women constituted Group E. Clinical data were collected for each group, and intergroup differences were analyzed. RESULTS: Compared with Group B, Group A exhibited significantly higher rates of intrapartum fever, cesarean delivery, and premature rupture of membranes (p < 0.05). Neonatal outcomes were also less favorable in Group A, with higher NICU admission rates and a greater incidence of pathological jaundice, as well as lower Apgar scores than in Group B (all p < 0.05). Within Group B, Group D had significantly higher rates of intrapartum fever, abnormal routine blood test results, meconium-stained amniotic fluid (≥ grade Ⅲ), and postpartum hemorrhage than Group C (p < 0.05); however, no significant differences in neonatal outcomes were observed between Groups C and D (p > 0.05). After excluding GBS-positive cases, Group E likewise showed higher rates of intrapartum fever, abnormal routine blood test results, and postpartum hemorrhage compared with Group C (p < 0.05), while neonatal outcomes did not differ significantly between Groups C and E (p > 0.05). CONCLUSIONS: Abnormal vaginal flora colonization is associated with an increased risk of maternal perinatal infection, without a corresponding increase in neonatal infection. These findings support the implementation of third-trimester vaginal flora screening and appropriate treatment for pregnant women planning vaginal delivery.