title: Placental cord insertion and birth weight discordancy in twin gestations.
abstract: OBJECTIVE
  To evaluate whether abnormal umbilical cord insertion (UCI) into the placenta is a risk factor for birth weight discordancy in twin gestations.
  
  
  METHODS
  Pathology records of all liveborn twins delivered between January 1993 and June 1996 were reviewed. The information collected included gestational age at delivery, birth weight, gross placental pathology, and placental UCI-velamentous, marginal, or disc. Discordancy in birth weight was defined as an intrapair difference of at least 20%. Analyses were stratified on placental chorionicity. Odds ratios and 95% confidence intervals for birth weight discordancy were calculated based on the presence of an abnormal (velamentous or marginal) placental UCI relative to normal (disc) UCI on both placentae, after adjusting for potential confounders.
  
  
  RESULTS
  There were 447 twin pairs identified. Dichorionic diamniotic placentation was present in 358 pairs (80.1%), monochorionic diamniotic in 84 (18.8%), and monochorionic monoamniotic in five (1.1%). There was a 13-fold increase in the risk of birth weight discordancy in monochorionic diamniotic twins in the presence of a velamentous UCI (odds ratio 13.5, 95% confidence interval 1.4, 138.4), with a rate of birth weight discordancy of 46%. This relationship was not demonstrated in dichorionic diamniotic twins (odds ratio 1.0, 95% confidence interval 0.3, 3.5).
  
  
  CONCLUSIONS
  Birth weight discordancy in twins is a different entity depending on chorionicity. The substantial increase in birth weight discordancy in monochorionic diamniotic twins that accompanies velamentous UCI underscores the need for prenatal detection and increased surveillance in these twins.
authors.affiliation: Department of Obstetrics, Gynecology, and Reproductive Services, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, St. Peter's University Hospital, New Brunswick, New Jersey 08903-0591, USA. hanleyml@umdnj.edu
authors.forename: Maryellen L
authors.initials: ML
authors.lastname: Hanley
authors.forename: Cande V
authors.initials: CV
authors.lastname: Ananth
authors.forename: Susan
authors.initials: S
authors.lastname: Shen-Schwarz
authors.forename: John C
authors.initials: JC
authors.lastname: Smulian
authors.forename: Yu-Ling
authors.initials: YL
authors.lastname: Lai
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Vintzileos
mesh_terms: D000328:Adult; D001724:Birth Weight; D002823:Chorion; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D010920:Placenta; D011247:Pregnancy; D011272:Pregnancy, Multiple; D012307:Risk Factors; D014427:Twins; D016216:Ultrasonography, Prenatal; D014470:Umbilical Cord