5Benirschke K,Kaufmann P.The pathology of the human placenta[J].New York:Springer-Verlag,1990,24:202-203.
6King DL.Placental migration demonstrated by ultrasonography.A hypothesis of dynamic placentation[J].Radiology,1973,109(1):167-170.
7Eichelberger KY,Haeri S,Kessler DC,et al.Placenta previa in the second trimester:sonographic and clinical factors associated with its resolution[J].Am J Perinatol,2011,28(9):735-740.
8Predanic M,Perni SC,Baergen RN,et al.A sonographic assessment of different patterns of placenta previa "migration" in the third trimester of pregnancy[J].J Ultrasound Med,2005,24(6):773-780.
9Magann EF,Evans SF,Miss J,et al.Placental implantation at 18 weeks and migration throughout pregnancy[J].South Med J,1998,91(11):1025-1027.
10Cho JY,Lee YH,Moon MH,et al.Difference in Migration of Placenta according to the location and type of placenta previa[J].Journal of Clinical Ultrasound,2008,36(2):79-84.