Central nervous system malformation stillbirths, maternal age and birth order.

Abstract

Substantial literature but no consensus of opinion exists on the associations between central nervous system (CNS) malformations and birth order and maternal age. These notes may serve to emphasize this disunity providing possibly a representative survey. The Registrars General of England and Wales and of Scotland publish the number of anencephalic stillbirths spina bifida stillbirths hydrocephalic stillbirths and all stillbirths occurring annually. They classify the data by parity and by maternal age. In the data for both Scotland and England and Wales the proportion of stillbirths which are anencephalic and hydrocephalic diminishes with both maternal age and parity. In the data for Scotland the proportion of stillbirths which are due to spina bifida seems not to show such clear evidence of trend but when the data for Scotland and England and Wales are pooled a similar trend shows clearly. Several explanations can be offered to explain the decline in the proportion of stillbirths which are due to CNS malformations: there may be a positive maternal age (or birth order) effect among stillbirths which causes other than CNS malformations; a CNS malformation stillbirth may deter further reproductive effort to a greater extent than do other stillbirths; women prone to bear CNS malformation stillbirths may be less fertile than other stillbirth prone women; and there may really be a negative maternal age (or birth order) effect in each of the major CNS malformations. It is argued that the 1st 2 suggestions are inadequate to explain the decline in the CNS malformation stillbirth proportions. Regarding differential fertility Dr. H.B. Newcombe provided raw data on this point. The data refer to 2340 sibships in British Columbia which produced at least 1 stillborn infant during the 1953-58 period. Among these were 197 sibships which produced an anencephalic stillbirth 68 of which produced a hydrocephalic stillbirth and 37 in which spina bifida was recorded either as the primary or secondary cause of a stillbirth. From fthese data all sibships in which the last stillbirth occurred within 280 days of the end of 1958 and all sibships in which the stated birth order maternal age and duration of follow-up were not in conformity were eliminated. This left 2018 sibships. It is possible to calculate the frequencies of subsequent maternities expected to occur in the CNS stillbirth sibships on the hypothesis that overall fertility in these sibships does not differ from that in the sibships of all stillbirths. The figures were so small that one cannot conclude with any certainty that any fertility differentials exist at all.