The findings, from a study of more than 3,000 Austrian women, show that despite the advent of modern contraception a woman's birth month influences her reproductive performance, just as it has been found to do within historic populations.
Lead researcher Dr Susanne Huber of the University of Veterinary Medicine in Vienna and her colleagues at the University of Vienna and the Medical University of Vienna, found that, on average, the number of children was lower among women of reproductive age born between June and August than in those born in any other month, although there was no association between birth month and childlessness.
"It partially confirms a study of pre-modern women in Canada, which found that women born in mid to late summer and early autumn had below average numbers of live-born children, although that also found that women born in April had fewer children. It also partially confirms a study of historic Dutch women that showed fewer children among women born in mid to late summer and early autumn," said Dr Huber.
"We found that the women born in July had 0.3 fewer children per woman than those born in December, or to put it another way, 13.4% fewer of the 2.24 mean number per woman overall. It indicates that despite the potential influence of modern life and the use of contraception, birth month effects on later reproductive performance are at least to some degree similar in pre-modern and contemporary women."
Dr Huber and colleagues studied women aged over 45 and born after 1945 who were on the Microcensus Austria data set a quarterly sample survey that has been carried out in one per cent of Austrian households since 1967 by Statistik Austria.
"In an earlier study looking at
Contact: Margaret Willson
European Society for Human Reproduction and Embryology