Brief communication: birth month influences reproductive performance in contemporary women.

BACKGROUND Season of birth has been reported to affect later reproduction in samples of pre-modern women and contemporary men. METHODS To examine whether the effect of birth date is also valid in contemporary women, we investigated the association between birth month and measures of reproductive performance (number of live-born children, % childless individuals) in a representative sample of contemporary Austrian women. RESULTS Among reproducing women, birth month is significantly associated with the number of live-born children (n = 2839, P = 0.032). On average, women born in summer months have fewer children than women born during the remainder of the year. No association between birth month and the percentage of childless individuals was found. CONCLUSIONS As has been reported in pre-modern women, month of birth also appears to affect later reproduction in contemporary women.