title: Determinants of perinatal mortality and serious neonatal morbidity in the second twin.
abstract: OBJECTIVE
  To identify potential determinants of perinatal mortality and neonatal morbidity among second twins relative to first twins.
  
  
  METHODS
  A retrospective cohort design was used to study twin deliveries in Nova Scotia from 1988 to 2002. Monoamniotic or conjoined twins and twin pairs with major congenital anomaly or antepartum fetal death of either twin were excluded. The primary outcome was a composite measure of perinatal mortality and neonatal morbidity, including birth asphyxia, respiratory distress, neonatal trauma, and infection. Risk of adverse outcome of second twins relative to first-born co-twins was determined by matched-pair analysis.
  
  
  RESULTS
  Of 1,542 twin pairs, the second twin was at greater risk of composite adverse outcome (relative risk [RR] 1.62, 95% confidence interval [CI] 1.38-1.9) than the first twin. This excess risk was evident independent of presentation, chorionicity, or infant sex but was associated with planned vaginal delivery, birth weight discordance, and prolonged interdelivery interval. Term second twins were less likely to suffer excess morbidity with elective cesarean (RR 1.0, 95% CI 0.14-7.10) than with planned vaginal delivery (RR 3.0, 95% CI 1.47-6.11). The major contributors to neonatal morbidity in the second twin were birth asphyxia at 37 weeks or later and respiratory distress syndrome at less than 37 weeks.
  
  
  CONCLUSIONS
  The second twin is at greater risk of adverse perinatal outcome than the first twin, independent of presentation, chorionicity, or infant sex. Planned vaginal delivery, birth weight discordance, and prolonged interdelivery interval increase this infant risk. Elective cesarean delivery at term may improve perinatal outcome for the second twin. However, the number of cesarean births required to prevent one case of composite adverse outcome, assuming causality, was 33.
authors.affiliation: Department of Obstetrics and Gynaecology and the Perinatal Epidemiology Research Unit, IWK Health Centre, Dalhousie University, Halifax, Nova Scotia, Canada. anthony.armson@iwk.nshealth.ca
authors.forename: B Anthony
authors.initials: BA
authors.lastname: Armson
authors.forename: Colleen
authors.initials: C
authors.lastname: O'Connell
authors.forename: Vidia
authors.initials: V
authors.lastname: Persad
authors.forename: K S
authors.initials: KS
authors.lastname: Joseph
authors.forename: David C
authors.initials: DC
authors.lastname: Young
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Baskett
mesh_terms: D000328:Adult; D001238:Asphyxia Neonatorum / Q000401:mortality; D001722:Birth Order; D001724:Birth Weight / Q000502:physiology; D002585:Cesarean Section / Q000379:methods / Q000401:mortality; D015331:Cohort Studies; D016001:Confidence Intervals; D036861:Delivery, Obstetric / Q000379:methods / Q000401:mortality*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D008297:Male; D009674:Nova Scotia; D016017:Odds Ratio; D011247:Pregnancy; D011256:Pregnancy Outcome; D012127:Respiratory Distress Syndrome, Newborn / Q000401:mortality; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors; D014427:Twins