title: Some observations on the decline in the United States dizygotic twinning rate.
mesh_terms: D001722:Birth Order; D001723:Birth Rate; D005260:Female; D005298:Fertility; D006801:Humans; D008297:Male; D008423:Maternal Age; D010298:Parity; D011247:Pregnancy; D014427:Twins; D014429:Twins, Dizygotic; D014481:United States