The epidemiology of preterm birth.

The immediate causes of preterm birth (preterm labor, PPROM, maternal complications, and fetal distress) are well-established. Similarly, the epidemiologic and medical risk factors discussed are well-known. Most risk factors, unfortunately, are not easy to modify. Furthermore, the connection between epidemiologic risks and preterm birth is often unclear. As this brief discussion of potential mediators linking risk status to preterm birth indicates, much more research is needed to define and assess potential mechanisms. It is unclear how important the five mediating factors chosen for presentation will prove to be or if other more significant mechanisms exist. However, as Eastman noted 40 years ago, "only when the factors causing prematurity are clearly understood, can any intelligent attempt at prevention be made."