Twin Births in Belgium (1960-1961): A statistical study

Abstract

SUMMARYThe present paper deals with an analysis of the statistics concerning twin births in a sample of the Belgian population in 1960 and 1961. The frequency of twin births is of 0.01198 (± 0.00043), the frequency of a DZ birth among twins is 0.65081. Mothers of twins generally are older than mothers with children resulting from single gestation, the age difference concerning, as could be demonstrated, the distribution of DZ twins with the exclusion of MZ twins: whereas the frequencies of the total amount of twin births and of the total amount of DZ births increase with the mother's age, being highest in the 35-39 age class, the frequency of MZ births seems to be independent of the mother's age. The frequency of twin births also increases with the order of birth or gestation. Given that the mother's age and the order of birth are correlated, the influence of one of the two factors involved upon the frequency of twin births could be determined by keeping the other factor constant; the data from Mac Arthur (1953) were used to that effect.Finally, a bibliographic survey revealed that whereas the frequency of DZ births is very variable, that of MZ births is more constant.