preterm birth naturally occurs as a result of preterm labor or preterm premature rupture of fetal membranes. In contrast, indicated preterm occurs when labor is initiated by medical intervention because of dangerous pregnancy complications. This chapter discusses several medical illnesses and conditions, such as low prepregnancy weight, obesity, a family history of spontaneous preterm birth, and short interpregnancy interval, and their relationships to preterm birth. The chapter also provides an overview of infertility treatments and the resulting risk of multiple gestations, which place women at a greater risk for preterm delivery.

Indicated preterm birth appears to share a number of risk factors with spontaneous preterm birth. In a cohort of more than 2,900 pregnant women, Meis and colleagues (1998) noted a relation between indicated preterm birth and müllerian duct abnormality (OR 7.02; 95% CI 1.69– 29.15, proteinuria at less than 24 weeks of gestation (OR 5.85; 95% CI 2.66–12.89), a history of chronic hypertension (OR 4.06; 95% CI 2.29– 7.55), a history of indicated preterm birth (OR 2.79; 95% CI 1.45–5.40), a history of lung disease (OR 2.52; 95% CI 1.32–4.80), previous spontaneous preterm birth (OR 2.45; 95% CI 1.55–3.89), age greater than 30 years (OR 2.42; 95% CI 1.57–3.74), being African American (OR 1.56; 95% CI 1.02–2.40), and working during pregnancy (OR 1.49; 95% CI 1.02–2.19). With the possibility of a significant heterogeneity of risk factors and etiologic overlap, studies of preterm birth should consider indicated and spontaneous preterm births both together and separately as outcomes of interest (Savitz et al., 2005).

A number of maternal medical conditions are associated with an increased risk of indicated preterm birth (Table 5-1). Maternal medical ill-