At the time of the study, Jing Wu and Zhu Li were with the Institute of Reproductive and Child Health, Peking University, Beijing, People’s Republic of China; Yuanli Liu was with the School of Public Health, Harvard University, Boston, Mass; Keqin Rao and Juncheng Qian were with the Center for Health Statistics Information, Ministry of Health, China; and Qi Sun was with the School of Public Health, Peking University.