Data collection
The demographic information and baseline characteristics including age, pre-pregnancy weight and height (pre-BMI calculated, kg/m2), final weight at delivery, blood pressure, gravidity, parity, history of disease (cardiovascular disease, diabetes mellitus, chronic hypertension and etc.), degree of education, profession, smoking and drinking habits, was collected by questionnaire. According to China cutoff points, pregnant women were classified as low weight (BMI < 18.5 kg/m2), normal weight (18.5 kg/m2 ≤ BMI ≤ 23.9 kg/m2) or overweight & obese (BMI ≥ 24.0 kg/m2). Gestational weight gain (GWG) was calculated as the difference value between final weight at delivery and pre-pregnancy weight. Gestational age was determined by combination of the last menstrual period and the early first trimester ultrasound. The diagnosis of GDM was made by the criterion of the International Association of the Diabetes and Pregnancy Study Groups (IADPSG): one or more of the following values is met or exceeded in the 75g Oral Glucose Tolerance Test (OGTT): fasting glucose, 5.10 mmol/L; 1-h glucose, 10.00 mmol/L; 2-h glucose, 8.50 mmol/L.