title: Proposal of a new parameter for diagnosing a low-lying placenta in the third trimester: The distance between the external os and placental edge.
abstract: OBJECTIVE
  To validate a new parameter of the distance between the external os (EO) and placental edge (PE) to diagnose a low-lying placenta in the third trimester.
  
  
  METHODS
  The study participants included 94 uncomplicated singleton pregnant women with cephalic presentation. These women were cared for in our hospital in 1998-2011, with a posterior low-lying placenta, which was diagnosed as the distance between the internal os (IO) and a PE of 0-3.0 cm at 34-36 weeks' gestation. Measurements of cervical length (CL) and the distances of IO-PE and EO-PE were performed using transvaginal ultrasonography at least twice at 28-30 weeks, 31-33 weeks, and 34-36 weeks. Changes in CL, and the IO-PE and EO-PE distances were analyzed.
  
  
  RESULTS
  CL and the IO-PE and EO-PE distances did not change prior to 31-33 weeks. CL was shortened and the IO-PE distance was increased after 31-33 weeks (p = 0.0001), but the EO-PE distance was unchanged.
  
  
  CONCLUSIONS
  The EO-PE distance is a promising parameter for diagnosis of low-lying placenta in the third trimester up to 36 weeks' gestation.
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, Fukuoka University, Fukuoka, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nojiri
authors.affiliation: Center for Maternal, Fetal and Neonatal Medicine, Fukuoka University Hospital, Fukuoka, Japan. Electronic address: ty-obgyn@cis.fukuoka-u.ac.jp.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yoshizato
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, Fukuoka University, Fukuoka, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Sanui
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, Fukuoka University, Fukuoka, Japan.
authors.forename: Ryota
authors.initials: R
authors.lastname: Araki
authors.affiliation: Center for Maternal, Fetal and Neonatal Medicine, Fukuoka University Hospital, Fukuoka, Japan.
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Obama
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, Fukuoka University, Fukuoka, Japan.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Shirota
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, Fukuoka University, Fukuoka, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Miyamoto
mesh_terms: D000328:Adult; D002584:Cervix Uteri / Q000000981:diagnostic imaging*; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D010920:Placenta / Q000000981:diagnostic imaging*; D010923:Placenta Previa / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011247:Pregnancy; D011256:Pregnancy Outcome; D011263:Pregnancy Trimester, Third; D011296:Prenatal Diagnosis / Q000379:methods; D012189:Retrospective Studies; D018570:Risk Assessment; D018709:Statistics, Nonparametric; D016216:Ultrasonography, Prenatal; D055815:Young Adult
keywords: external os; internal os; low-lying placenta; placental edge; ultrasonography