The influence of obstetric intervention on trends in twin stillbirths: United States, 1989–99

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Abstract
Objective: Although twin stillbirth rates have declined substantially over the past two decades, the contribution of changes in obstetric interventions to reducing twin stillbirths has not been quantified. Methods: We carried out a retrospective cohort study of twin live births and stillbirths in the United States between 1989 and 1999 (n = 1 102 212). Changes in the rate of stillbirth ( ⩾ 22 weeks) before and after adjustment for changes in labor induction, Cesarean delivery and sociodemographic factors were estimated through ecological logistic regression analysis. This analysis was based on aggregating data by each state within the United States. Results: Between 1989 and 1999, rates of labor induction and Cesarean delivery among twin live births increased by 138% (from 5.8% to 13.8%) and 15% (from 48.3% to 55.6%), respectively. These changes were accompanied by a 43% decline in the stillbirth rate between 1989 and 1999 (from 24.4 to 13.9 per 1000 fetuses at risk). After excluding births weighing < 500 g, rates of labor induction among twins at 22–27 weeks', 28–33 weeks' and ⩾ 34 weeks' gestation increased by 95%, 131% and 127%, respectively, between 1989 and 1999. Cesarean delivery rates also increased by 55%, 29% and 2% in these same gestational age categories. The 48% (relative risk (RR) 0.52, 95% confidence interval (CI) 0.49–0.55) decline in stillbirth rate between 1989–91 and 1997–99 was reduced to a 25% (RR 0.75, 95% CI 0.72–0.79) decline after adjustment for changes in labor induction and Cesarean delivery. The decline in the rate of twin stillbirths was larger at later gestational ages (at ⩾ 32 and ⩾ 34 weeks) where the largest absolute increases in labor induction rates were observed. Conclusions: The use of Cesarean delivery and especially labor induction for twin pregnancies has increased substantially in the United States over the last decade and these changes have been associated with a large decline in the rate of stillbirth among twins.