Fertility of mothers with twins.
D000293:Adolescent; D000328:Adult; D001722:Birth Order; D005191:Family Characteristics; D005197:Famous Persons; D005260:Female; D005298:Fertility; D005387:Finland; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D013548:Sweden; D014427:Twins