Participants
We recruited reproductive-age women who participated in National Free Preconception Health Examination Project (NFPHEP) from January 2015 to September 2017 in Dongguan of Guangdong province of China. The details of the NFPHEP were described elsewhere (25). Briefly, women intended pregnancy within six months, were provided with free preconception examinations by well-trained health workers, including a standardized questionnaire and laboratory examinations. Then, the subsequent pregnancy outcomes of women (number of fetus, infant outcome, birthweight, gestation, date of delivery, etc.) were follow-up from medical records. Basic information included demographic characteristics (maternal age, nation, levels of education, height, weight, BMI, etc.), lifestyle (history of passive smoking, work condition of exposure to radiation/heat/organic solvent/heavy metal/ pesticides/other toxic substances etc.), history of choric disease (diabetes, hypertension, thyroid disease, heart disease, anemia), reproductive history (spontaneous/induced abortion, stillbirth, pregnancy, parity, etc.). In strict accordance with National Guide to Clinical Laboratory Procedures, serum FPG level of women was detected by glucose oxidase or hexokinase methods in the local laboratories, and accepted the external quality assessment and quality control biannually (26).
This study was approved by the Ethical Committee of Maternal and Children Health Care Hospital of Donguan City. The informed consents were obtained from each participant.