Trends in twin preterm birth subtypes and impact on perinatal mortality: United States, 1989 through 2000


      The rate of preterm birth among twins has increased substantially in recent years. We examined the rates of and trends in twin preterm birth following ruptured membranes (ROM), medically-indicated preterm birth, and preterm birth following spontaneous onset of labor (PTL). We further examined whether the recent decline in twin perinatal mortality was associated with trends in preterm birth subtypes.

      Study design

      We carried out a retrospective cohort study of 1,172,405 twin live births and stillbirths born in the United States between 1989 and 2000. Temporal trends in preterm birth <37 weeks, their subtypes, and perinatal mortality (stillbirths at ≥22 weeks plus neonatal deaths within 28 days), were examined through logistic regression models before and after adjusting for socio-demographic and behavioral factors. Results were analyzed separately for whites and blacks.


      The rate of twin preterm birth <37 weeks among white women increased from 43.5% in 1989 to 56.8% in 2000, and from 52.8% in 1989 to 61.2% in 2000 among blacks. Medically-indicated preterm birth increased by 49% (95% confidence interval (CI) 48%, 51%) among whites, and by 30% (95% CI 27%, 33%) among blacks. PTL and preterm birth following ROM increased by 38% and 15%, respectively, among whites, whereas among blacks, PTL and preterm birth following ROM increased by 9% and 17%, respectively. The increase in preterm birth among twins was strongly associated with a decline in perinatal mortality (P < .001). Perinatal mortality declined the most for medically-indicated preterm births (41%) among whites, but the decline in mortality among blacks was greatest in the PTL group (38%).


      Temporal trends in preterm birth among twins varied substantially based on underlying subtypes and maternal race. The recent increase in medically-indicated preterm birth among twins is associated with a large and favorable reduction in perinatal mortality among twin gestations.