BackgroundGive the high background risk of adverse pregnancy outcomes (APOs), it is important to understand the associations of maternal pre-pregnancy body mass index (ppBMI), gestational weight gain (GWG) with APOs in women with gestational diabetes mellitus (GDM). We addressed the independent and joint associations of maternal ppBMI and GWG with APOs in Chinese women with GDM.Methods764 GDM women with singleton delivery were studied and they were stratified into three weight groups by ppBMI (underweight, normal weight and overweight/obesity) following classification standards for Chinese adults and three GWG groups (inadequate, adequate, excessive GWG) by the 2009 Institute of Medicine guidelines, respectively. Univariate and multivariate logistic regression analyses were performed to estimate the odds ratios of APOs.ResultsMaternal overweight/obesity was associated with increased odds of pregnancy-induced hypertension [PIH, adjusted odds ratio (aOR): 2.828, 95% confidence interval (CI) 1.382–5.787], cesarean delivery (CS) (aOR 2.466, 95%CI 1.694–3.590), preterm delivery (aOR 2.466, 95%CI 1.233–4.854), LGA (aOR 1.664, 95%CI 1.120–2.472), macrosomia (aOR 2.682, 95%CI 1.511–4.760) and any pregnancy complication (aOR 2.766, 95%CI 1.840–4.158) compared with healthy weight. Inadequate GWG was less likely to develop PIH (aOR 0.215, 95%CI 0.055–0.835), CS (aOR 0.612, 95%CI 0.421–0.889) and any pregnancy complication (aOR 0.628, 95%CI 0.435–0.907), but had higher risk of preterm birth (aOR 2.261, 95%CI 1.089–4.692), while excessive GWG was more vulnerable to LGA (aOR 1.929, 95%CI 1.272–2.923), macrosomia (aOR 2.753, 95%CI 1.519–4.989) and any pregnancy complication (aOR 1.548, 95%CI 1.006–2.382) as compared to adequate GWG. Furthermore, compared to normal weight mothers with adequate GWG, obese mothers with excessive GWG had the highest risk of any pregnancy complication (aOR 3.064, 95%CI 1.636–5.739).ConclusionsMaternal overweight/obesity and GWG were associated with APOs in the already high-risk settings of GDM. Obese mothers with excessive GWG may confer the greatest risk of adverse outcomes. It was very helpful to reduce the burden of APOs and benefit GDM women by promoting a healthy pre-pregnancy BMI and GWG.