title: Recurrence of preterm birth in twin pregnancies in the presence of a prior singleton preterm birth.
abstract: OBJECTIVE
  We examined recurrence of preterm birth in twin pregnancy in the presence of a previous singleton preterm pregnancy, and assessed if these recurrence risks differed for medically indicated and spontaneous preterm birth.
  
  
  METHODS
  A retrospective cohort study was designed using the maternally-linked data of women who delivered a first singleton live birth followed by a twin birth in the second pregnancy (n = 2329) in Missouri (1989--97). We examined preterm birth recurrence at <37 in the second twin pregnancy among women with a prior singleton preterm birth. Recurrence risks were based on hazard ratios (HR) and 95% confidence intervals (CI) estimated from Cox proportional hazards models after adjusting for potential confounders.
  
  
  RESULTS
  Preterm birth rates in the second twin pregnancy were 69.0% and 49.9% among women who had a previous preterm and term singleton birth, respectively (HR 1.8, 95% CI 1.6-2.1). The preterm birth rate in the second pregnancy was about 95% when the first singleton pregnancy ended at <30 weeks. Women delivering preterm following a medical intervention in the first pregnancy had increased recurrence for both spontaneous (HR 1.4, 95% CI 1.1-2.0) and indicated (HR 2.4, 95% CI 1.8-3.2) preterm birth; similarly among women with a prior spontaneous preterm birth, hazard ratios were 1.8 (95% CI 1.5-2.1) and 1.6 (95% CI 1.3-1.9), for spontaneous and indicated preterm birth in the second twin pregnancy, respectively.
  
  
  CONCLUSIONS
  Women with a singleton preterm birth carry increased risk of preterm birth in the subsequent twin pregnancy. A history of a singleton preterm birth has an independent and additive contribution to risk of preterm birth in the subsequent twin gestation.
authors.affiliation: Division of Epidemiology and Biostatistics, Department of Obstetrics, Gynecology, and Reproductive Sciences, UMDNJ-Robert Wood Johnson Medical School, New Brunswick, New Jersey 08901, USA. cande.ananth@umdnj.edu
authors.forename: Cande V
authors.initials: CV
authors.lastname: Ananth
authors.forename: Russell S
authors.initials: RS
authors.lastname: Kirby
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Vintzileos
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D008923:Missouri / Q000453:epidemiology; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D012008:Recurrence; D012189:Retrospective Studies; D014427:Twins