Impact of meconium-stained amniotic fluid thickness on maternal infectious morbidity: a comprehensive clinical and microbiological analysis

Purpose: The aim of this study was to investigate the correlation between the thickness of meconium-stained amniotic fluid (MSAF) and maternal infectious morbidity. Methods: A retrospective study of 15,950 term singleton pregnancies at a tertiary hospital (2020–2024). Women were categorized into four groups based on the presence and thickness of MSAF: clear, light, intermediate, and thick. The co-primary outcomes were clinical chorioamnionitis and puerperal endometritis, defined as a composite maternal infectious morbidity. In women with intrapartum fever (IPF), chorioamniotic swabs were obtained and compared according MSAF thickness. Multivariate analysis identified predictors of a composite maternal infections and adverse neonatal outcomes. Results: Of the cohort, 13,745 had clear amniotic fluid, and 2,205 had MSAF (561 light, 1,426 intermediate, 218 thick). The incidence of maternal infections increased with MSAF thickness, with thick MSAF showing the highest rates of clinical chorioamnionitis (4.1%, p < 0.001) and endometritis (1.4%, p = 0.039). In IPF cases, thicker MSAF was associated with a higher prevalence of positive swab cultures, particularly of Enterobacteriaceae (61.9%). Group B Streptococcus (GBS) remained consistent across all MSAF groups. Multivariate analysis showed that MSAF levels were associated with increased maternal infectious morbidity (p < 0.001). Additional risk factors for maternal infections included nulliparity (p < 0.001), catheter balloon insertion (p = 0.004), prolonged ROM (p < 0.001), and cesarean delivery (p < 0.001). In contrast, only intermediate (p < 0.001) and thick MSAF (p < 0.001) correlated with adverse neonatal outcomes. Conclusion: Greater severity of MSAF is associated with increased maternal infectious morbidity, especially infections related to Enterobacteriaceae. Studies about preventive measures in cases of thick MSAF are warranted.