Psychobiological Stress and Preterm Birth

Abstract

Despite current research progress, preterm birth (delivery before 37 weeks gestation) remains a significant problem in maternal-child health because of its high prevalence rate and association with severe adverse health consequences (March of Dimes, 2009; Goldenberg et al., 2000; Sibai et al., 2005; Ventura et al., 2000). Globally, an estimated 13 million babies are born preterm each year representing a 9.6% prevalence of preterm birth (March of Dimes, 2009). The incidence and consequences of preterm birth (PTB) are particularly high and harsh in Africa and Asia where over 11 million (85%) of all preterm births occur. Preterm birth is the leading cause of infant morbidity and mortality. About one million deaths in the first month of life (or 28 percent of total newborn deaths) are attributable to preterm birth. In the United States (US) preterm birth occurs in 10-15% of all pregnancies and the rate has increased by 35% in the past 25 years (March of Dimes, 2009; Institute of Medicine, 2006). There is a significantly higher rate of preterm birth among African-American women (17.8%) compared to Caucasian women (8.8%) (Institute of Medicine, 2006). In the US, preterm births are associated with 75% of perinatal mortality (Adams & Barfield, 2008; Nathanielsz, 1995; Novy et al., 1995). Long term follow-up indicates that between one-third to one-fifth of preterm children have moderate to severe sensory handicaps by age two (including cerebral palsy, mental retardation, epilepsy, blindness or deafness) (Escobar et al., 1991; Kramer, 2009; Kuban & Leviton, 1994). Because of this the economic consequences of PTB are of similar magnitude as smoking, alcohol abuse and AIDS (Novy et al., 1995). An Institute of Medicine (2006) report estimated the cost of PTB to be $26.2 billion in 2005 with daily NICU costs exceeding $3,500 per infant, and it is not unusual for costs to top $1 million for a prolonged stay (Catlin, 2006). Despite the magnitude of this problem, the etiology of preterm birth remains poorly understood. The precise mechanisms by which human parturition is initiated spontaneously, either at term or preterm, are not well understood (Kramer et al., 2009). It is established that microbial colonization and inflammation in the maternal genital tract is one cause of preterm birth (Gibbs et al., 1992) and account for the majority of preterm births between 21 and 24 weeks. As gestation progresses to 33 weeks, however, the incidence of preterm birth due to infection drops below 10%. Thus, in the large majority of preterm births there is no known etiological agent. While the exact causes of preterm labor are not known, they may include behavioral, environmental, biological and psychosocial factors, medical conditions and genetics. As described above, there are striking racial-ethnic and socioeconomic