Trends and characteristics of induced labour in the United States, 1989-98.

Induction of labour is one of the fastest growing medical procedures in the United States. In 1998, 19.2% of all US births were a product of induced labour, more than twice the 9.0% in 1989. Induction of labour has been efficacious in the management of post-term pregnancy and in expediting delivery when the mother or infant is sufficiently ill to make continuation of the pregnancy hazardous. However, the recent rapid increase in induction, and particularly the doubling of the induction rate for preterm pregnancies (from 6.7% in 1989 to 13.4% in 1998), has generated concern among some clinicians. The present study uses vital statistics natality data to examine the epidemiology of induced labour in the US. Multivariable analysis is used to examine the probability of having an induced delivery in relation to a wide variety of socio-demographic and medical characteristics, and also in relation to relative indications and contraindications for induced labour as outlined by the American College of Obstetricians and Gynecologists (ACOG). Induction rates were higher for women who were non-Hispanic white, college educated, born in the US, primaparae and those with intensive prenatal care utilisation. Induction rates were also higher for women with various medical conditions including hypertension, eclampsia and renal disease. For non-Hispanic white women with singleton births, 59% of the increase in the preterm birth rate from 1989 to 1998 can be accounted for by the increase in preterm inductions. The adjusted odds ratio for neonatal mortality among preterm births with induced labour was 1.20 [95% confidence interval 1.11, 1.31]. The rapid increase in induction rates, particularly among preterm births, marks a shift in the obstetric management of pregnancy. More detailed studies are needed to examine physician decision-making protocols, particularly for preterm induction, and to assess the impact of these practice changes on patient outcomes.