title: Twinning rates and the "pill".
mesh_terms: D003276:Contraceptives, Oral / Q000494:pharmacology*; D003280:Contraceptives, Oral, Synthetic / Q000494:pharmacology*; D005260:Female; D006801:Humans; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000187:drug effects*; D013997:Time Factors; D014427:Twins
chemical_list: D003276:Contraceptives, Oral; D003280:Contraceptives, Oral, Synthetic