Peking University - Beijing International Center for Mathematical Research, Peking University - School of Mathematical Sciences, Peking University - School of Mathematical Sciences, Peking University - School of Mathematical Sciences, Peking University - School of Mathematical Sciences, Peking University - Department of Biostatistics, University of Nottingham, Ningbo - Department of Chemical and Environmental Engineering, National Research Institute for Health and Family Planning, Capital Medical University - Beijing Obstetrics and Gynecology Hospital and Peking University - Center for Statistical Sciences