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Risk factors for preterm labor and delivery

Julian N Robinson, MD
Errol R Norwitz, MD, PhD
Section Editor
Charles J Lockwood, MD, MHCM
Deputy Editor
Vanessa A Barss, MD, FACOG


Multiple genetic, environmental, and immunological factors contribute to a woman’s likelihood of preterm delivery; interactions between genetic

susceptibility and environmental stimuli must also play a role. Preterm labor likely results from local changes that prematurely stimulate the cascade of events resulting in spontaneous labor or prematurely withdraw suppressive factors that maintain uterine quiescence and thus inhibit this cascade. The four major pathogenic pathways leading to preterm labor are intrauterine infection, decidual hemorrhage, excessive uterine stretch, and maternal or fetal stress.

There are many risk factors for preterm labor and delivery (table 1). Increasing evidence suggests that these risk factors are markers of dysfunctional immunological defense within the tissues of the uterus and this dysfunction is the root cause preterm labor [1].

Some risk factors 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


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