Racial disparities in preterm birth rates and short inter-pregnancy interval: an overview.

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.