title: Analysis of twinning rates in Japan.
mesh_terms: D000293:Adolescent; D000328:Adult; D001722:Birth Order; D001723:Birth Rate; D005260:Female; D005313:Fetal Death / Q000209:etiology; D006801:Humans; D007564:Japan; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D018566:Pregnancy, High-Risk; D011272:Pregnancy, Multiple; D012621:Seasons; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic