Epidemiology of twin pregnancy.
D001827:Body Height; D001835:Body Weight; D003276:Contraceptives, Oral / Q000494:pharmacology; D005260:Female; D005300:Fertility Agents, Female / Q000494:pharmacology; D006801:Humans; D008423:Maternal Age; D010298:Parity; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000187:drug effects; D012923:Social Class; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
D003276:Contraceptives, Oral; D005300:Fertility Agents, Female