BACKGROUND: It remains unclear how pre-pregnancy body mass index (BMI) affects preeclampsia in the Chinese population, primarily due to insufficient large-scale research on this topic. OBJECTIVE: The study aimed to determine the relationship between pre-pregnancy BMI and (severe) preeclampsia in the Chinese population, providing a detailed description of the findings. METHODS: The retrospective study included a total of 75,773 pregnant women registered between 2016 and 2020. These participants were categorized into four groups based on their pre-pregnancy BMI: underweight (BMI <
18.5 kg/m RESULTS: A lower risk of developing preeclampsia was observed in the underweight population, with an OR of 0.604 (95%CI, 0.507-0.719). In contrast, women who were overweight or obese during the pre-pregnancy period demonstrated a significantly higher risk of preeclampsia, with ORs of 2.211 (95%CI, 1.967-2.486) and 3.662 (95%CI, 3.026-4.431), respectively. After adjusting for confounding factors, the elevated risk of preeclampsia persisted, showing ORs of 2.152(95%CI, 1.911-2.425) for the overweight population and 3.493 (95%CI, 2.874-4.245) for those who were obese, while the risk for underweight women remained lower, with an OR of 0.609(95%CI, 0.511-0.727). For severe preeclampsia, the risk was also higher in the overweight and obese participants after adjusting for confounders, demonstrating ORs of 1.652(95%CI, 1.364-2.001) and 2.762(95%CI, 2.014-3.788), respectively. The underweight population exhibited a lower risk of severe preeclampsia, with an OR of 0.720(95%CI, 0.565-0.919). In addition, these risks were not significantly associated with maternal age. CONCLUSION: Regardless of adjustment for confounders, underweight women demonstrated a lower risk of preeclampsia, whereas the overweight/obese population exhibited a higher occurrence of both preeclampsia and severe preeclampsia. These associations were not influenced by maternal age.