A survey of twins in the population of a prospective collaborative study.
D000293:Adolescent; D000328:Adult; D005006:Ethnicity; D005260:Female; D005313:Fetal Death; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D011247:Pregnancy; D012959:Socioeconomic Factors; D014427:Twins