title: Does sonographic determination of placental location predict fetal birth weight in diamniotic-dichorionic twins?
abstract: OBJECTIVE
  The purpose of this study was to determine the association between placental location in diamniotic-dichorionic twins as determined at the time of anatomic survey and birth weight.
  
  
  METHODS
  We retrospectively identified all diamniotic-dichorionic twins in our Maternal-Fetal Medicine sonography database between 2000 and 2005 who had an anatomic survey, went on to be delivered at our hospital, and had records available for review (n = 304). Placental location for each twin was determined at the time of anatomic survey and grouped into both anterior or both posterior versus separate anterior and posterior. Maternal and fetal characteristics were collected from chart review. Placental pathologic findings were available for 249 (83%) patients. Outcomes analyzed were percent discordance, small size for gestational age of twin A or B, and difference in birth weight as a continuous variable. Multivariable logistic regression using stepwise backward elimination was used to adjust for potential confounders.
  
  
  RESULTS
  There was no difference in discordance of 20% or greater or incidence of small size for gestational age when both placentas were both anterior and both posterior compared with separate anterior and posterior: adjusted odds ratio (AdjOR), 1.38 (95% confidence interval [CI], 0.64-2.95); and AdjOR, 1.29 (95% CI, 0.57-2.89). The actual birth weight difference (A - B) was not affected by placental location (P = .36). Opposite sex fetuses and nulliparity were significantly associated with birth weight discordance: AdjOR, 2.68 (95% CI, 1.39-5.17); and AdjOR, 0.34 (95% CI, 0.28-0.94).
  
  
  CONCLUSIONS
  We did not find a correlation between birth weight and placental location in our cohort analysis. The presence of sex-discordant twins was associated with birth weight discordance of 20% or greater, whereas nulliparity was protective.
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology, and Reproductive Sciences, Mount Sinai Medical Center, 5 E 98 St, Second Floor, Box 1171, New York, NY 10029-6574 USA. victoria.belogolovkin@mssm.edu
authors.forename: Victoria
authors.initials: V
authors.lastname: Belogolovkin
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Engel
authors.forename: Lauren
authors.initials: L
authors.lastname: Ferrara
authors.forename: Keith A
authors.initials: KA
authors.lastname: Eddleman
authors.forename: Joanne L
authors.initials: JL
authors.lastname: Stone
mesh_terms: D000328:Adult; D001724:Birth Weight; D005260:Female; D006801:Humans; D009518:New York / Q000453:epidemiology; D010920:Placenta / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D011379:Prognosis; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014429:Twins, Dizygotic; D016216:Ultrasonography, Prenatal / Q000706:statistics & numerical data*