Analysis of multiple birth rates in Japan. V. Seasonal and social class variations in twin births.
D001723:Birth Rate; D005260:Female; D005313:Fetal Death / Q000453:epidemiology; D006801:Humans; D007564:Japan; D008297:Male; D011247:Pregnancy; D012621:Seasons; D012959:Socioeconomic Factors; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic