Abstract: Objective：To assess the influence of preconception over-weight and obesity on gestational weight gain and other pregnancy prognosis. Methods：We collected data of singleton pregnancies delivered in our hospital from Jan 2015 to Dec 2017. All cases were divided into three groups(over-weight, obese and normal-weight) according to preconception body mass. Comparison was conducted among the three groups on the weight gain during pregnancy and pregnancy related prognosis. By multivariate analysis, the effect of preconception over-weight and obese on weight gain during pregnancy and other pregnancy outcome were clarified. Results：1 080 cases with complete data were included: 496 overweight cases, 44 obese cases and 540 control cases. The preconception BMI of over-weight, obese and normal-weight group were 26.3(2.0) kg/m2, 31.3(2.9) kg/m2 and 20.7(2.5) kg/m2 respectively. The over-weight and obese groups developed more above-gainers than the normal weight group(63.9%,72.7% vs. 41.3%). The risks of pre-eclampsia, GDM, cesarean section were higher than the normal weight group. The over-weight and obese group demonstrated higher average birth weight [(3 528.0±397.4) kg, (3 562.6±417.6) kg vs. (3 387.8±384.5 kg)] and high risk of macrosomia (12.3%, 15.9% vs. 5.0%). By multivariate analysis, preconceptional over-weight (OR=3.071, 95%CI: 2.345-4.022) and obese (OR=5.113, 95%CI: 2.507-10.431) exerted significant effect on the risk of exceeding the Institute of Medicine(IOM) recommended weight gain range and also the risk of pre-eclampsia, GDM, cesarean section and macrosomia. Conclusions：Preconception over-weight and obesity has significant influence on the result of gestational weight gain(especially the risk of over-gainer) and perinatal outcomes including pre-eclampsia, GDM, cesarean section and macrosomia. Therefore it is crucial to initiated body weight control before pregnancy especially for overweight and obese women.

Key words: Body mass index, Preconception care, Prenatal care, Overweight, Obesity, Weight gain, Pregnancy outcome, Pregnancy complications