title: Embryo reduction and birth weight discordance in dichorionic twins.
abstract: BACKGROUND
  Twin birth weight discordance is associated with a poor perinatal outcome. The aim of this study was to analyse the risk factors of growth discordance among dichorionic twin pregnancies.
  
  
  METHODS
  A cohort of 346 dichorionic twin pregnancies delivered at one perinatal centre between January 1996 and December 1999 was analysed. Two groups were created, according to the presence or absence of intra-pair birth weight discordance (n = 75 and 271 respectively). Birth weight discordance was defined as a difference of >/=20% of the weight of the heavier twin. The two groups were compared by uni- and multivariate analysis, with regard to the woman's characteristics, risk factors for growth restriction or discordance, and outcome of pregnancy.
  
  
  RESULTS
  Pregnancies with birth weight discordance had a poor outcome compared with pregnancies without discordance, with a 4-fold increase in neonatal mortality. The rate of iatrogenic embryo reduction was significantly higher in discordant pregnancies (14.7 versus 6.6%, P = 0.03). The risk of birth weight discordance was increased with a larger starting number of embryos before reduction [20.2% (64/317), 28.6% (6/21), 57.1% (4/7) and 100% (1/1) respectively, for an initial number of two (no reduction), three, four, and five embryos, P = 0.02]. In multivariate analysis, embryo reduction was the only significant risk factor for the occurrence of birth weight discordance [adjusted odds ratio (OR) = 2.3 (1.0-5.2)].
  
  
  CONCLUSIONS
  Birth weight discordance carries a poor perinatal outcome. Embryo reduction is an independent risk factor for birth weight discordance in dichorionic twins. This finding emphasises the need for better control of assisted reproductive technology in order to avoid high-order multiple pregnancies.
authors.affiliation: Department of Obstetrics and Gynecology, Hôpital Antoine Béclère, Assistance Publique Hopitaux de Paris, Université Paris XI, 92140 Clamart, France. francois.audibert@abc.ap-hop-paris.fr
authors.forename: François
authors.initials: F
authors.lastname: Audibert
authors.forename: Marine
authors.initials: M
authors.lastname: Boullier
authors.forename: Claire
authors.initials: C
authors.lastname: Boithias
authors.forename: Violaine
authors.initials: V
authors.lastname: Kerbrat
authors.forename: Michèle
authors.initials: M
authors.lastname: Vial
authors.forename: René
authors.initials: R
authors.lastname: Frydman
mesh_terms: D000328:Adult; D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D011247:Pregnancy; D018607:Pregnancy Reduction, Multifetal / Q000009:adverse effects*; D018570:Risk Assessment; D014429:Twins, Dizygotic