Additional considerations limit generalizability of findings. Our sample is predominantly Caucasian and given often substantial race differences in both AD risk (Grant, 1997; Hassin et al., 2007) and timing of first childbearing (Martin, Hamilton, Sutton, Ventura, Menacker, & Munson, 2003), it is possible that patterns of AD-related reproductive delay differ for other populations. Observed patterns might also differ cross-nationally. Athough international comparisons of AD prevalence are difficult because of diagnostic differences and differences in whether prevalence for lifetime versus past year prevalence is reported (WHO, 2004), reproductive onset varies widely even among developed countries, with average age at first childbirth in Australia among the oldest (ABS, 2007).
