Gynaecology & Obstetrics Complication of 3rd Stage of Labour 7988b8da Common cause of retained placenta: A Atonic uterus B Constriction ring C Placenta accreta D Poor voluntary expulsive effort High-Yield Explanation Ans. is a, i.e. Atonic uterusRef. JB Sharma Obs, Pg 343M/C cause of retained placenta is a simply adherent placenta. This is due to mainly atonic uterus.