Categories of Pre-pregnancy BMI
Pre-pregnancy BMI was calculated by dividing the weight in kilogram (kg) by the square of the height in meters (m), and was classified into four categories based on Chinese criteria12: underweight (BMI <18.5kg/m2), normal weight (18.5-23.9kg/m2), overweight (24.0-27.9kg/m2), and obesity (≥28.0kg/m2).