Clustering of twin births in space and time.
Out of a total of 1025 twin births occurring in 11 South Moravian districts from 1972 to 1976, 638 occurred in the same time and space interval (P = 0.00037). The observed clustering suggests the existence of environmental factors influencing twinning rates.
D003604:Czechoslovakia; D005260:Female; D006801:Humans; D011247:Pregnancy; D013029:Space-Time Clustering; D014427:Twins