There are many risk factors for preterm labor and delivery (table 1). Some are reversible, others are permanent. Identification of risk factors for spontaneous preterm birth (PTB) before conception or early in pregnancy ideally would lead to interventions that could help prevent this complication. However, this goal has been elusive for several reasons:
- The causality of purported risk factors has been difficult to prove. Some obstetrical complications resulting in PTB require cofactors to exert their effect, further complicating the chain of causality
- Many PTBs occur among women with no risk factors at all
- An adequate animal model for study of PTB does not exist.
Risk factors for preterm labor and delivery will be reviewed here. Pathogenesis, prediction, treatment, and prevention of preterm labor and delivery are discussed separately:
History of preterm birth — Some risk factors for preterm birth (PTB) likely persist from pregnancy to pregnancy. Prior PTB is the strongest risk factor for future PTB, and recurrences often occur at the same gestational age [1-3]. However, most women who have had a PTB will have subsequent pregnancies of normal duration [2,4-7].