Follow up
All the participated women were followed up by trained local community health worker by telephone every two months to determine whether they had conceived successfully. Local health worker interviewed the women face to face or by telephone within three months after conception, documenting their last menstrual period, active smoking, alcohol consumption, and husband smoking during the early stage of the pregnancy. Women were also interviewed face to face or by telephone within six weeks of delivery to collect information on the hospital where delivery took place. Local community health workers then collected data from the medical records at the reference hospital regarding pregnancy outcomes, including gestational age (weeks), birth weight (grams), obstetrical outcomes (caesarean delivery, shoulder dystocia or birth injury), neonatal information (singleton or multiple births and sex) and stillbirth (only collected from 46 counties in 13 cities).
All of these baseline data and fellow up data were transferred to Guangdong Institute of Family Planning Science and Technology where they were cleaned, complied and de-identified. The endpoint of this study was to observe the pregnancy outcomes of the participated mothers and the study was terminated on 31st December 2017.