Incidence of twin births in Denmark from 1911 to 1974.
A survey of twin births in Denmark in relation to the total number of births from 1911 to 1974 shows a significant decrease in the dizygotic twin birth rate for all maternal age groups. The possible environmental causes of such a decrease are discussed.
D000328:Adult; D003718:Denmark; D005260:Female; D006801:Humans; D008297:Male; D008423:Maternal Age; D011247:Pregnancy; D011272:Pregnancy, Multiple; D014310:Triplets; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic