title: Letter: Twinning and oral contraceptives.
mesh_terms: D003276:Contraceptives, Oral / Q000494:pharmacology*; D005260:Female; D006801:Humans; D011247:Pregnancy / Q000187:drug effects; D011272:Pregnancy, Multiple; D013223:Statistics as Topic; D014427:Twins
chemical_list: D003276:Contraceptives, Oral