Abstract： Objective:To investigate the associations between pre-pregnancy body mass index (BMI) and occurrence and clinical features in pregnant women complicated by preeclampsia (PE).Methods:We recruited 42 427 pregnant women who were diagnosed with intrauterine pregnancy at Shenzhen Maternity and Child Healthcare Hospital from July 2017 to December 2019, with a gestational age of 6~8 +6 weeks, excluding those with basic diseases and incomplete medical records. Among them, 659 were diagnosed with PE. According to the pre-pregnancy BMI, the pregnant women were divided into underweight group (42 cases), normal body weight group (422 cases), overweight group (138 cases) and obesity group (57 cases). Maternal outcomes (the occurrence of preeclampsia, cesarean delivery rate) and neonatal outcomes (birth weight, Apgar score and neonatal ICU admission) were recorded. The maternal outcomes, gestational age of delivery, delivery mode, newborn birth weight, Apgar score and admission to neonatal ICU were compared among the pregnant women in each group. Logistic regression model was established to analyze the influence of different pre-pregnancy BMI on the occurrence and clinical features of PE. Results:The incidence of PE was 1.55% (659/42 427), and the incidence of PE was 0.61% (42/6 941), 1.44% (422/29 297), 2.62% (138/5 273) and 6.22% (57/916) in the underweight group, the normal weight group, the overweight group and the obesity group, respectively. After adjustment for age, parity, educational level, history of preeclampsia, and in vitro fertilization and embryo transfer (IVF-ET), compared with normal group, the adjusted OR for developing early-onset PE were 0.57 (95% CI: 0.29-1.02) for underweight, 1.03 (95% CI: 0.65-1.56) for overweight and 2.15 (95% CI: 1.03-4.02) for obesity groups. The OR for developing late-onset PE were 0.50 (95% CI: 0.33-0.72) for underweight, 1.57 (95% CI: 1.23-1.99) for overweight and 4.25 (95% CI: 3.00-5.91) for obesity group. The OR for PE without severe features were 0.54 (95% CI: 0.30-0.89), 1.40 (95% CI: 0.97-1.99) and 5.11 (95% CI: 3.22-7.84) for underweight, overweight and obesity groups, respectively. The OR for severe PE were 0.51 (95% CI: 0.33-0.75), 1.42 (95% CI: 1.10-1.83) and 2.97 (95% CI: 1.95-4.38) for underweight, overweight and obesity groups, respectively. The median neonate birth weight in women with PE were 2 420 g (1 602-2 845 g), 2 435 g (1 692-3 030 g), 2 540 g (1 922-3 132 g), and 2 950 g (2 050-3 360 g) for underweight, normal, overweight and obesity groups, respectively. The neonatal birth weight in obesity group was heavier than that in normal group ( P<0.05). The incidence rates of large for gestational age (LGA) in PE women were 0 (0/42), 3.3% (14/422), 7.3% (10/138) and 17.5% (10/57) for underweight, normal, overweight and obesity groups, respectively. The incidence rate of LGA in obesity group was higher than that in normal group ( P<0.05). Conclusions:Pre-pregnancy obesity is an independent risk factor for PE. Obesity related PE is more likely associated with late-onset PE and LGA. It is recommended to control weight before pregnancy, limit weight gain during pregnancy and control blood pressure to reduce the incidence of PE and ensure the safety of mother and child.