Objective. We seek to expand on a biopsychosocial framework underlying the etiology of excess preterm birth experienced by African-American women by exploring short inter-pregnancy intervals as a partial explanatory factor. Design. We conducted a qualitative analyses of published studies that met specified criteria for assessing the association of inter-pregnancy interval and preterm birth. Methods. We determine whether inter-pregnancy interval is associated with preterm birth, what the underlying causal mechanism may be, whether African-American women are more likely than Caucasian women to have short intervals, and whether achieving an optimal interval will result in reduced African-American-Caucasian gap in preterm births. Main Outcome Measures. Crude and adjusted odds ratios for preterm birth, with the referent group being the interval closest to the 'ideal' of 18-23 months and the exposed group having intervals < 12 months or some subset of that inter-pregnancy interval. Results. Inter-pregnancy interval less than six months increases preterm birth by about 40%. The mechanism may be through failure to replenish maternal nutritional stores. While there may not be an interaction between race and short inter-pregnancy interval, short intervals can explain about 4% of the African-American-Caucasian gap in preterm birth because African-American women are approximately 1.8 times as likely to have inter-pregnancy intervals of less than six months. Limited studies indicate that optimal intervals can be achieved through appropriate counseling and health care. Conclusions. Excess risk for preterm birth may be reduced by up to 8% among African-Americans and up to 4% among Caucasians through increasing inter-pregnancy intervals to the optimal length of 18-23 months.