Twinning in relation to the marital status of the mother.
D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D007086:Illegitimacy; D008423:Maternal Age; D008875:Middle Aged; D010060:Ovulation; D011247:Pregnancy; D012537:Scandinavian and Nordic Countries; D014427:Twins