“…Some idea of this can be derived, however, from the findings of the Royal Commission on Population (1950) and of the 1951 Census, and from data concerning patients attending antenatal clinics (reviewed by Bender, 1952) and those attending infertility clinics (Westman, 1950 ;Grant, 1951;Bender, 1952;Barns et al, 1953 ;Southam and Buxton, 1957;Sharman, 1958 ;Wilson et al, 1959;Wyper, 1962). The material is somewhat heterogeneous and does not permit of precise conclusions.…”