a1 MRC Mammalian Development Unit, University College London
a2 Department of Biology, North East London Polytechnic, London
Variations in sex ratio with maternal age, paternal age, parity and time have been examined in data on all legitimate births (live and stillbirths) in England and Wales, 1968–77. There were significant linear declines in sex ratio with both increasing parity and increasing paternal age, and a curvilinear relationship with maternal age. These effects were largely independent. Before 1955 it seems likely that sex ratio declined with increase in maternal age. But it seems that between 1955 and 1968 there was an unexplained decline in the sex ratio of births to women aged 20–24 and an increase in that of births to women aged 30–34. There was no significant secular trend in sex ratio during the period 1968–77.
(Received July 15 1983)