Recent Statistics of Multiple Births in England and Wales

Abstract

Analysis of the statistics of multiple births in England and Wales between July, 1938 and December, 1945 proves that the frequency of monozygotic twin births is virtually constant, at about 3 per 1000 pregnancies, for all ages of mothers. The frequency of dizygotic twinning, however, increases with maternal age from 2 per 1000 pregnancies at 17 to a maximum of 14 per 1000 pregnancies at 38, and then decreases gradually to 5 per 1000 maternities at 45. Comparison of the average numbers of previous children to mothers at each age shows that the twin pregnancies were associated with a greater number of previous children then were the single maternities. While the reasons for this difference cannot be deduced from this data, if the tendency to multiple births is governed entirely by heredity and is independent of a woman’s parity, this greater number of previous children to mothers of twins vould indicate that the probability of repetition of a twin birth is ten times as large as he total population frequency of twins births.