cially anxiety over the pregnancy itself, as a risk factor for preterm delivery. In contrast, recent prospective studies on depression do not suggest a strong pattern for depression as a risk factor for preterm delivery; rather, these studies indicate that prenatal maternal depression may predict birth weight and fetal growth. The emerging literature on racism and preterm delivery suggests that racism, a possible stressor throughout the lifetimes of African American women, contributes to the explanation for racial-ethnic disparities in the rates of both preterm birth and low birth weight.
The results of more than two decades of observational studies on naturally occurring social support do not confirm a hypothesized link between maternal social support and preterm delivery; however, the studies do provide fairly consistent evidence for a direct association between social support and infant birth weight. Similarly, the provision of additional support to pregnant women during controlled intervention studies has not reduced the likelihood that the mother will give birth too early, although it does appear to have other benefits for women’s health care and psychosocial adjustment. The few available studies on maternal self-esteem, mastery, and optimism provide little evidence for associations with preterm birth specifically, although the concept of perceived control may be a risk factor. Finally, preliminary research on the association of the intendedness of the pregnancy and preterm delivery suggests that women with unintended pregnancies are more likely to deliver their infants preterm.
The foregoing reviews and discussion of behavioral and psychosocial factors involved in the etiology of preterm birth give rise to some suggested future directions for researchers:
At present, many studies of birth outcomes do not use preterm birth as a study outcome. Instead low birth weight is often used as a proxy. As stated earlier in this report (see Chapter 2), low birth weight can be caused by both preterm birth and fetal growth restriction, two conditions with some overlapping but also divergent determinants and pathways. Future research needs to define preterm birth and small for gestational age as specific and distinct study outcomes and should not use low birth weight as a proxy for preterm birth. In addition, attention should be paid to whether the onset of labor is spontaneous.
Studies of behavioral risk factors and preterm birth should examine constellations of lifestyle factors rather than individual behaviors in isolation to elucidate possible etiologic pathways for specific subtypes of preterm delivery.
Studies of stress and preterm birth should focus on specific components or factors, such as anxiety and hypothesized pathways from this condition to preterm birth. There is a pressing need for more theoretical analyses on the intensity and duration of distinguishable emotional states and