Alternate changes in birth seasonality of twins during 1971-1984 in Japan.
Birth dates of 1,536 twin-pairs in 1971-1984 were collected from the members of an association of twins' mothers. The seasonal variation of twinning changed every 2-4 years. Years when twinning rate was higher in the summer-fall season (1971-72, 1976-77, 1982-84) and those when a peak of the rate was not observed (1973-75, 1978-81) appeared alternately. In years with a summer-fall peak, the elevation of twinning in the summer-fall season was detected consistently in both like- and unlike-sexed and in both MZ and DZ twin groups. The twinning seasonality in these years, however, was not evident in twin births of mothers who were born in May-July. These results suggest the possibility that seasonal factors which influence the twinning rate be not multiple-ovulation-inducing but probably abortion-inducing factors and most likely seasonally epidemic microbes.
Nakamura
I
I
Department of Hygiene, Teikyo University School of Medicine, Tokyo, Japan.
Amau
Y
Y
Nonaka
K
K
Miura
T
T
D000022:Abortion, Spontaneous / Q000453:epidemiology; D001723:Birth Rate; D005260:Female; D049673:History, 20th Century; D006801:Humans; D007564:Japan; D011247:Pregnancy; D012621:Seasons; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic