4Grannum PAT,Berkowitz RL,Hobbins JC.The ultrasonic change in the maturing placenta and their relation relation to fetal pulmonic maturity.Am J Obstet Gynecol 1979,133(8):915-922. 被引量:1
5Fox H.Calcification on the placenta .J Obstet Gynaecol Br Commonw.1964,71(2):759-765. 被引量:1