Gender of offspring after oral-contraceptive use.

We examined the sex of offspring born after oral-contraceptive use according to duration of contraceptive use and the interval between cessation of use and conception for 6109 live births. The overall proportion of male births (with 90 per cent confidence) falls between 0.491 and 0.512. These data exclude with high probability a shift in the sex distribution of the magnitude previously hypothesized, and are not consistent with even a moderate shift in sex distribution. Sex of offspring was not related to total duration of oral-contraceptive use, duration of use since any previous pregnancy or interval between termination of use and conception. It appears that oral contraceptives have no bearing on the sex of subsequent offspring.