Objective: We examined the hypothesis that black race independent of other factors increases the risk for extreme preterm birth and its frequency of recurrence at a similar gestational age.
Study design: We conducted a population-based cohort study using the Missouri Department of Health's maternally linked database of all births in Missouri between 1989 and 1997 for factors associated with recurrent preterm delivery.
Results: Recurrent black preterm births occurred at increased frequency (adjusted odds ratio 4.11 [95% confidence interval 3.78 to 4.4.47]) and earlier gestations (31 versus 33 weeks' median age) than white births. Black siblingships also had higher multiplicity of prematurity (odds ratio 2.14 [95% confidence interval 1.49 to 3.07] and 5.09 [95% confidence interval 1.26 to 20.51] for 3 and 4 preterm births). Additionally, 47% of women delivered recurrent preterm infants within 2 weeks of the gestational age of their initial preterm infant.
Conclusion: Overrepresentation of preterm births in blacks occurs independently of maternal medical and socioeconomic factors. Furthermore, the grouping of timing for preterm birth in different pregnancies of the same mother implicates important genetic contributors to the timing of birth.