The association between venous thromboembolism during pregnancy and low birth weight: A retrospective cohort study

Abstract Background Among the causes of maternal morbidity and mortality worldwide, venous thromboembolism (VTE) also impacts long-term effects on some organs beyond physical harm of pregnancy. Evidence on the effect of VTE on neonatal outcomes, especially low birth weight (LBW), is still insufficient and contradicting. The objective of this study was to assess the relationship between maternal VTE during pregnancy and LBW in a large national cohort. Methods In a retrospective cohort study, we used data from the Sina Health Information System covering 21094 pregnant women who had received standard prenatal care in Mashhad, Iran from March 2017 to September 2025. The exposed group included 10547 women with VTE confirmed that were each individually matched (1:1) to non exposed pregnant women without a record of VTE. The analysis was performed in Stata version 16. Multivariate logistic regression analysis was used to calculate adjusted odds ratios (AORs) and 95% confidence intervals (CIs) for LBW (< 2500 g) confounders such as mothers education, parity, hypertensive disorders, antepartum haemorrhage and previous miscarriage were considered. Results Low birth weight was significantly more frequently recorded in a group of infants whose mothers had VTE compared to a group of infants whose mothers did not have VTE (59% compare to 41%, P < 0.001). Even after the adjustment for confounders, VTE remained a powerful independent factor for LBW (AOR = 2.28, 95% CI: 2.08–2.50, P < 0.001). Besides VTE, maternal hypertension was one of the independent predictors included maternal hypertension (AOR = 1.74, 95% CI: 1.50–2.03), vaginal bleeding during pregnancy (AOR = 1.45, 95% CI: 1.15–1.87) and history of recurrent miscarriage (≥ 3 abortions; AOR = 2.22, 95% CI: 1.72–2.86). Conversely, higher maternal education was associated with a protective effect against LBW. Conclusion Maternal VTE during pregnancy is a significant and independent risk factor for low birth weight likely mediated through impaired placental perfusion and inflammatory pathways. These findings underscore the need for early risk assessment, timely diagnosis and optimized management of thromboembolic disorders during pregnancy to improve neonatal outcomes. Further studies are warranted to explore mechanistic pathways and evaluate the impact of preventive anticoagulant interventions.