Kistka ZA, et al. Racial disparity in the frequency of recurrence of preterm birth. Am J Obstet Gynecol. Feb 2007;196(2):131.e1-131.e6.
This study examined the hypothesis that independent of other factors, being black increased the risk of extreme preterm birth and its frequency of recurrence at a similar gestational age. The study found that recurrent black preterm births occurred at increased frequency and at an earlier gestation age (median age: 31 weeks versus 33 weeks), when compared with white births.