Sex ratio and parental age gap.

We tested the hypothesis that a large age difference between parents can shift the sex ratio at birth in favor of males as [J. T. Manning et al. published in Nature Vol. 389 p. 344 1997] suggested in their analysis of English and Welsh data. Among children born in Lombardy (northern Italy) in 1990 and 1991 we observed an anomalous excess of males born to a particular subsample of parents with a wide age gap [more than 15 years] between them; in the overall sample the father-mother age gap does not significantly contribute to the determination of the childs sex. (EXCERPT)