Baseline
The NFPHEP was based on the primary health and family planning network. All the reproductive couples who had planned to conceive were recruited. Baseline information was collected by trained local community health workers, which included demographic characteristics (age, educational level, occupation, ethnicity, migration and address of residence), history of chronic disease (hypertension, diabetes, heart disease, chronic nephritis, anaemia, cancer and psychiatric diseases), history of pregnancy (gravidity and parity) and history of adverse pregnancy outcomes (preterm birth, miscarriage, induced abortion, birth defect and stillbirth), lifestyle (maternal active smoking, passive smoking, alcohol consumption and husband smoking). Clinical professionals from the local authorized medical institutions then did physical examinations. Body weight and height were measured by calibrated instruments with standard measurement procedures.11