The Incidence of Human Multiple Births

Abstract

1. Statistics on more than 120,000,000 cases of labor were obtained from official sources in twenty-one countries, and the percentages of the various types of multiple births were computed from them. 2. The percentage of multiple births was found to vary greatly for different countries. The twin percentage ranged from 1.59 per cent in Denmark to .40 per cent. in Colombia, and the triplet percentage from .0185 per cent. in Denmark to .0040 per cent. in Greece. 3, Twin confinements were found to occur once in 85.2, triplet confinements once in 7,628.7 and quadruplet confinements once in 670,734 cases of labor in this study covering 120,061,398 pregnancies. These results agree essentially with findings of the earlier and less extensive investigations of Guzzoni and of G. Veit and also with the estimate of Arey. This agreement seems to indicate a fixed relationship between the incidence of the various types of human gestations. 4. A general agreement was noted between the twin and triplet percentages in the individual countries. Those countries having a large twin percentage had also ,a large triplet percentage, while those reporting few cases of twine reported also few cases of triplets. 5. The total twin, triplet and quadruplet ratios were found to be respectively 1: 85.2; 1: (87.3)2, and 1: (87.5)3. These values very closely approach those expected according to Zeleny's hypothesis that, if 1/n is the proportion of twin births to all births in a large population, then the proportion of triplet births and the proportion of quadruplet births for the same period will approximate respectively 1/n2 and l/n3. In conclusion, the writer wishes to acknowledge his indebtedness to the officials of the various countries whose cooperation in furnishing authentic statistics made this paper possible. Especial thanks are due, also, to Professor Ira E. Cutler, of the University of Denver, under whose direction this study was begun, and to Professor Francis Ramaley, of the University of Colorado, whose encouragement and helpful suggestions have aided greatly in the preparation of the manuscript.