3Hendricks MS,Chow YH,Bhagavath B,et al,Previsous cesarean section and abortion as risk factors for developing placenta previa [J].J Obstet Gynaecol Res,1999,25 (2): 137-142.
4James WH.Placenta previa:preponderance of male sex at birth[J].Am J Epidemiol,2000,152(2) :195-196.
5Mortensen JT,Thulstrup AM, Larsen H, et al.Smoking, sex of offspring, and risk of placental abruption,placenta previa and preeclampsia:a population-based cohort study[J].Acta Obstet Gynecol Scand, 2001,80 (10) : 894-898.
