title: The Twinning and Fertility Paradox.
mesh_terms: D001722:Birth Order; D001723:Birth Rate; D003276:Contraceptives, Oral / Q000494:pharmacology; D010064:Embryo Implantation; D005191:Family Characteristics; D005260:Female; D005298:Fertility; D006801:Humans; D008297:Male; D011247:Pregnancy; D011272:Pregnancy, Multiple; D013997:Time Factors; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
chemical_list: D003276:Contraceptives, Oral