title: A sonographic assessment of different patterns of placenta previa "migration" in the third trimester of pregnancy.
abstract: OBJECTIVE
  The purpose of this study was to compare the rates and patterns of placental "migration" with the mode of fetal and placental delivery and the incidence of peripartum complications.
  
  
  METHODS
  This was a retrospective study of 163 cases of placenta previa diagnosed by transvaginal sonography at 28 weeks' gestation that were followed serially by sonography. The patients were stratified into 3 groups depending on the placenta-to-internal cervical os distance: (1) an overlap of 0.0 cm or greater over the cervical os, (2) 0.1 to 2.9 cm, and (3) 3.0 cm or greater. The mean rate of placental migration (millimeters per week) was obtained at 28 to 32 and 32 to 36 weeks' gestation. A pattern of placental migration was classified as one with acceleration or deceleration of the placental migration in the late third trimester based on a comparison between the migration rates at 28 to 32 and 32 to 36 weeks' gestation.
  
  
  RESULTS
  At the time of delivery, 22, 29, and 112 patients were included in groups 1, 2, and 3, respectively. The rates of placental migration correlated with the final placental distance from the internal cervical os (0.1 to 4.1 mm/wk for groups 1 and 3, respectively). Significantly higher rates of interventional cesarean delivery (CD) (P=.0002), elective CD (P=.0254), manual placenta removal (P=.0419), and placenta accreta (P=.0039), but not CD for indications other than placenta previa (P=.0752), were associated with a placental distance of less than 2.0 cm away from the cervix and a deceleration pattern of placental migration. In contrast, vaginal delivery was significantly associated with a placental distance of 2.0 cm or greater away from the cervix and an acceleration pattern of placental migration (P=.0034).
  
  
  CONCLUSIONS
  A final placental distance of less than 2.0 cm from the internal cervical os and a deceleration pattern of placental migration were significantly associated with an interventional CD and a higher rate of peripartum complications.
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Weill Medical College of Cornell University, New York, NY 10021, USA. mlp2001@med.cornell.edu
authors.forename: Mladen
authors.initials: M
authors.lastname: Predanic
authors.forename: Sriram C
authors.initials: SC
authors.lastname: Perni
authors.forename: Rebecca N
authors.initials: RN
authors.lastname: Baergen
authors.forename: Claudel
authors.initials: C
authors.lastname: Jean-Pierre
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Chasen
authors.forename: Frank A
authors.initials: FA
authors.lastname: Chervenak
mesh_terms: D036861:Delivery, Obstetric; D005260:Female; D006801:Humans; D010923:Placenta Previa / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011256:Pregnancy Outcome; D011263:Pregnancy Trimester, Third; D012189:Retrospective Studies; D014463:Ultrasonography