The Impact of First-Trimester Vaginal Microecology on Spontaneous Abortion: A Retrospective Cohort Study

Background: Spontaneous abortion is a complex multifactorial disease. Recently, vaginal microbiota has become a research hotspot for understanding the etiology of spontaneous abortion. Here, we aimed to explore associations of first-trimester vaginal microecology with adverse pregnancy outcomes. Methods: A retrospective cohort study included 786 pregnant women receiving prenatal care at Fujian Maternity and Child Health Hospital between 2023 and 2025. All participants underwent vaginal microecological examinations. Study outcomes included abortion, preterm birth (PTB), prelabor rupture of the membranes (PROM), intrapartum fever, meconium-stained amniotic fluid, etc. The logistic regression analysis was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the associations between vaginal microecological parameters and these outcomes. Results: Of 786 participants, 160 (20.4%) had spontaneous abortion, and 626 (79.6%) delivered. The mean vaginal Lactobacillus proportion was significantly lower in the spontaneous abortion group (42.5 ± 35.85%) than in the non-abortion group (61.6 ± 26.72%; p < 0.001). After age adjustment, vulvovaginal candidiasis (VVC) (OR = 2.17, 95% CI = 1.34–3.52, p = 0.001), bacterial vaginosis (BV) (OR = 3.19, 95% CI = 1.89–5.38, p < 0.001), and moderate-to-severe aerobic vaginitis (AV) (OR = 2.71, 95% CI = 1.08–6.82, p = 0.034) were associated with elevated spontaneous abortion risk. Among enzymatic markers, inflammation-related leukocyte esterase was also associated with higher spontaneous abortion risk (OR = 2.22, 95% CI = 1.39–3.61, p < 0.001). In addition, BV was significantly associated with PROM (OR = 2.95, 95% CI = 1.50–5.79, p = 0.002). Conclusion: Reduced Lactobacillus abundance and pathogenic proliferation linked to BV and VVC constitute a risk factor for spontaneous abortion. These findings suggest the potential clinical value of vaginal microecological monitoring in early-trimester pregnancy.