Risk factors associated with the occurrence of preterm birth.

Epidemiologic studies have demonstrated associations between preterm birth and several biologic, behavioral, and social factors. However, preterm birth as a phenomenon has not changed very much over time, and the differences between populations are not as great as one would expect, if one takes into account the vast differences in the occurrence of the known risk factors. The implication is that knowledge about some of the most significant risk variables is still lacking. Hence, there is a need to collect more detailed information, particularly on behavioral and social variables, which may indicate new risk factors. In addition, well-designed intervention studies may provide new insights into cause-and-effect relationships with regard to preterm birth. A number of such studies have recently been designed and have begun collecting data. An increased understanding of the etiology of preterm birth will undoubtedly result from these clinical trials and related research efforts. The development of some effective means to prevent or reduce the occurrence of preterm delivery with its associated high risk for perinatal mortality will depend upon the successful conduct and completion of these intervention studies.