Assessment of covariates and outcome definition
Pre-pregnancy body mass index (BMI) was calculated by dividing self-reported pre-pregnancy weight (kg) by height squared (m2). According to the International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria26, gestational diabetes mellitus (GDM) was diagnosed when OGTT fasting ≥ 5.1 mmol/L or OGTT 1 hour ≥ 10.0 mmol/L or OGTT 2 hour ≥ 8.5mmol/L. The date of last menstrual period was used to estimate gestational age (in weeks). PTB was defined as gestational week less than 37 weeks.