Risk of stillbirth in twin pregnancy related to sex and maternal age; an analysis of 90,386 twin maternities.

It is well known that in every country with reliable vital statistics more male than female children are born each year, and that the sex ratio of stillbirths is considerably higher than that of related live births. By means of data from the Annual Reports of the Registrar-General for England and Wales and for Scotland it has recently been demonstrated (Lowe and McKeown, 1950) that the sex ratio of total births decreases with maternal age, whereas the sex ratio of stillbirths increases. It was suggested that this relationship to age is due to changes in the relative proportions in each maternal age group of different causes of stillbirth, each of which has its own sex ratio. Since July, 1938, the Annual Reports of the Registrar-General for England and Wales have presented the results of twin maternities by sex, type of birth (live or stillborn), and maternal age, although cause of stillbirth is unfortunately not recorded. Between July, 1938, and December, 1948, 90,730 twin maternities were notified, for 344 of which maternal age was not specified. We are unaware of any reference in the literature to the sex of twin stillbirths in relation to the age of the mother, and this communication presents an analysis of 90,386 twin maternities for which the necessary data are available.