title: Risk of preterm delivery and growth restriction in twins discordant for structural anomalies.
abstract: OBJECTIVE
  We sought to determine whether twin gestations with an anomalous fetus are at increased risk of preterm delivery or intrauterine growth restriction (IUGR) compared to twins with 2 normal fetuses.
  
  
  METHODS
  This was a retrospective cohort of twins undergoing ultrasound 15-22 weeks' gestation. Groups were defined by the presence of 1 twin with a major anomaly (discordant) or by twins with no major anomalies (normal). The primary outcomes were preterm delivery (<37 weeks) and IUGR (<10th percentile).
  
  
  RESULTS
  Of 1977 twin pregnancies, 66 had a twin with a major anomaly. Preterm delivery occurred in 42 (63.6%) discordant twins, compared to 1271 (66.5%) normal twins (risk ratio, 1.0; 95% confidence interval, 0.8-1.2). IUGR was diagnosed in 15 (22.7%) normal co-twins, compared to 406 (21.3%) presenting twins in normal twins (risk ratio, 1.1; 95% confidence interval, 0.7-1.7).
  
  
  CONCLUSIONS
  Twins discordant for major anomalies are not at increased risk of preterm delivery or IUGR compared to twins with no major anomalies.
authors.affiliation: Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine, MO, USA.
authors.forename: Lorie M
authors.initials: LM
authors.lastname: Harper
authors.forename: Anthony O
authors.initials: AO
authors.lastname: Odibo
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Roehl
authors.forename: Ryan E
authors.initials: RE
authors.lastname: Longman
authors.forename: George A
authors.initials: GA
authors.lastname: Macones
authors.forename: Alison G
authors.initials: AG
authors.lastname: Cahill
mesh_terms: D000328:Adult; D004200:Diseases in Twins / Q000453:epidemiology*; D005260:Female; D005317:Fetal Growth Retardation / Q000453:epidemiology*; D005333:Fetus / Q000002:abnormalities*; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D007234:Infant, Premature; D011247:Pregnancy; D011256:Pregnancy Outcome; D059285:Pregnancy, Twin / Q000706:statistics & numerical data*; D047928:Premature Birth / Q000453:epidemiology*; D012189:Retrospective Studies; D012306:Risk; D055815:Young Adult