1. From the Department of Health Statistics (Y.W., Y.X.), Fourth Military Medical University, Xi’an, China; Department of Primary Health Care (Y.W., C.H., R.P., N.R., P.G., C.B.) and National Perinatal Epidemiology Unit (J.H.), Department of Public Health, University of Oxford, Oxford, United Kingdom; and Health Care Evaluation Group (J.H.), Department of Epidemiology and Public Health, University College London, London, United Kingdom.