摘要：Objectives. We examined the relationship between obstetrical intervention and preterm birth in the United States between 1991 and 2006. Methods. We assessed changes in preterm birth, cesarean delivery, labor induction, and associated risks. Logistic regression modeled the odds of preterm obstetrical intervention after risk adjustment. Results. From 1991 to 2006, the percentage of singleton preterm births increased 13%. The cesarean delivery rate for singleton preterm births increased 47%, and the rate of induced labor doubled. In 2006, 51% of singleton preterm births were spontaneous vaginal deliveries, compared with 69% in 1991. After adjustment for demographic and medical risks, the mother of a preterm infant was 88% (95% confidence interval [CI] = 1.87, 1.90) more likely to have an obstetrical intervention in 2006 than in 1991. Using new birth certificate data from 19 states, we estimated that 42% of singleton preterm infants were delivered via induction or cesarean birth without spontaneous onset of labor. Conclusions. Obstetrical interventions were related to the increase in the US preterm birth rate between 1991 and 2006. The public health community can play a central role in reducing medically unnecessary interventions. During the past 15 years, rates of obstetrical interventions have been rising in the United States. 1 , 2 The percentage of births with induced labor more than doubled between 1991 and 2006, from 10.5% to 22.5%. 1 , 2 After a decline in the early 1990s, the cesarean delivery rate increased by 50%, from 20.7% in 1996 to an all-time high of 31.1% in 2006. 1 Large increases occurred for both primary and repeat cesarean deliveries and among mothers with no known medical risk factors or indications for cesarean delivery (such as diabetes, hypertension, or premature rupture of membranes). 1 , 3 , 4 Recent studies have shown that changing primary cesarean rates did not correspond to shifts in mothers’ medical risk profiles but, rather, appeared to be related to increased use of cesarean delivery with all medical conditions. 4 – 6 From 1991 to 2006, the preterm (less than 37 weeks of gestation) birth rate increased by 19%, from 10.8% to 12.8% of all births 1 ; the preterm rate increased by 13% for singletons and by 22% for multiple births. An increase in the preterm birth rate is of concern because rates of death and disability are higher among preterm infants than among infants born at term (37–41 weeks). 7 – 9 Although rates of death and disability are highest among infants born very preterm (less than 32 weeks), mortality rates among moderately preterm (32–33 weeks) and late preterm (34–36 weeks) infants are 7 and 3 times, respectively, the mortality rates for term infants. 7 We examined the relationship between changes in the use of obstetrical intervention and changes in the preterm birth rate in the United States between 1991–2006. Specifically, we explored trends in singleton preterm births, delivery methods (cesarean or vaginal), and induction of labor.
