• We used data from the population-based Metropolitan Atlanta Congenital Defects Program to study the epidemiology of the early amnion rupture spectrum of defects. For the period 1968 through 1982, we identified 45 patients among 388 325 live births, for a birth prevalence rate of 1.16 per 10000. The prevalence for male infants was 0.91 and for female infants, 1.44. The defects occurred 1.76 times more often in blacks than in whites (95% confidence interval 0.98, 3.13). Infants of young, black multigravidas (20 years, more than one pregnancy) showed the highest rate (6.2), and infants of older, black multigravidas showed the lowest rate (0.5) (rate ratio = 12.4, 95% confidence interval 4.2, 36.4). These findings suggest that young, black multigravidas are at much higher risk than are older, black multigravidas of having infants with this spectrum of defects. Ascertainment (diagnostic) differences between hospitals probably account for some of the racial discrepancy in birth prevalence, but they do not explain the maternal age effects in black multigravidas. Because the higher rates for blacks probably reflect more accurate diagnoses, the findings also suggest that a closer estimate of the true birth prevalence may be about 3 per 10000 live births.