Eub 5500

Self-reported pregravid weight was recorded on the day of registration. Body weight was measured with an ultrasonic meter (Dingheng, Zhengzhou, China) to the nearest 100 g by trained nurses according to standard procedures at enrollment and at regular intervals (in 4-week intervals from enrolment to week 25, every 2-week until week 33 weekly thereafter) to birth (Figure 1). These information and maternal height (measured to the nearest 0.1 cm by trained nurses at enrollment) were recorded in the Medical Birth Registry.
For all participants, gestational age (GA) was assessed during the first ultrasound scan (Eub 5500, Hitachi; Eub 7500, Hitachi; Logiq E9, GE) on the day of registration, which was conducted in a standard manner by trained ultrasonographers. GA was estimated by combining ultrasonography data with self-report on the last menstrual period: if both measures were available and there was agreement (±14 days) self-report data was used, otherwise, ultrasound data were used.

A self-administered questionnaire was used to collect information on age, residence, occupation, education level and personal income of the participants at P1. In addition, reproductive history, medical history, and family history of chronic diseases were assessed by this questionnaire. Gestational age (GA) was assessed during the first ultrasound scan (Eub 5500, Hitachi; Eub 7500, Hitachi; Logiq E9, GE) on the day of registration. GA was estimated by combining ultrasonography data with self-reports on the last menstrual period. If both measures were available and they were in agreement (± 14 days) then self-reported data were used, otherwise ultrasound data were used.