Definition
Pre-pregnant body mass index (pre-BMI) was calculated as dividing the pre-pregnant body weight (kilograms) by the square of height (meters), and classified into underweight (<18.5 kg/m2), normal weight (18.5-22.9 kg/m2) and overweight/obesity (≥23 kg/m2) based on the Asia-Pacific classification of BMI5.
According to the diagnostic criteria, which was founded by the Chinese Medical Association in 2014, GDM was diagnosed when any serum glucose value equaled or exceeded the thresholds during OGTT:fasting blood glucose (FBG), 5.1 mmol/l; 1 hour, 10.0mmol/l; and 2 hour, 8.5mmol/l. However, FBG≥7.0mmol/l or 2 hour result≥ 11.1mmo/l was considered as pre-gestational diabetes mellitus (PGDM), and then excluded from our study6.
Gestational hypertension was defined as new-onset hypertension (systolic blood pressure≥140 mmHg and/or diastolic blood pressure≥90 mmHg) after 20 weeks of gestation in the absence of proteinuria, which returned to normal within 12 weeks after delivery7. PE was the progression of GH, which was defined as new-onset hypertension with albuminuria (≥ 0.3g protein of urine in 24 hours or positive detection of random urine protein) or other biochemical or haematological abnormalities.
Postpartum hemorrhage was defined by the International Federation of Gynecology and Obstetrics 8 criteria (24 hours postpartum bleeding ≥ 500 ml in vaginal delivery; ≥ 1000 ml in caesarean delivery).
Small for gestational age (SGA) was defined as neonatal birth weight less than the 10thpercentile for gestational age, while LGA was above the 90th percentile; both of them were based on the Chinese Neonatal Birth Weight Curve for Different Gestational Age9. PTB was defined as gestational age at delivery smaller than 37 weeks10.