The relationship of socioeconomic status to preterm contractions and preterm delivery.

Spontaneous preterm labor precedes approximately 50% of preterm births. One to 10% of pregnant women are hospitalized for preterm labor. This study examines the relationship of socioeconomic indicators, family income, education and type of insurance, with preterm contractions and subsequent preterm delivery. Data were from the pregnancy risk assessment monitoring system on 107,926 women who had singleton births during 2000-2002. Data on preterm contractions, family income, and type of insurance during pregnancy were from the maternal questionnaire. Maternal education and gestational age were derived from birth certificate data. Predicted marginal probabilities from logistic regression models were used to calculate the adjusted cumulative incidence and cumulative risk ratio of preterm contractions and preterm delivery. Median annual household income was approximately $30,000. More than one-fourth (28.1 95% CI: 27.7, 28.6) of women experienced preterm contractions, and these women were 3 times as likely (18 vs. 5%) to deliver preterm as women without preterm contractions. Only 58% of women who delivered preterm reported contractions. Lower income and Medicaid-paid care were independently associated with an increased risk of preterm contractions but not with preterm delivery. The association of lower income and Medicaid enrollment with preterm contractions but not preterm delivery suggests that SES is associated with the initiation of the pathway to spontaneous preterm delivery rather than access to or the success of interventions to prevent delivery following the onset of contractions.