Concordance in timing of preterm (20–34 6/7 weeks’ gestation) birth in Missouri to a mother with previous preterm birth, 1989–1997. The line represents the expected Gaussian curve if concordance in timing is a normally distributed event. The bars represent the timing for each preterm birth after the initial preterm birth for A, all mothers, B, Caucasians, or C, African American in correlation with the expected normal curve. (Reproduced with permission from Kistka et alx, with permission.)
Kistka ZA, Palomar L, Lee KA, Boslaugh SE, Wangler MF, Cole FS et al. Racial disparity in the frequency of recurrence of preterm birth. Am J Obstet Gynecol 2007;196:131.