Imaizumi Y
Institute of Population Problems, Ministry of Health and Welfare, Tokyo, Japan.
Acta Genet Med Gemellol (Roma). 1987;36(3):325-34. doi: 10.1017/s0001566000006073.
The twinning rate remained nearly constant up to 1968, then decreased in 1974 and gradually increased with the year. The triplet birth rate remained nearly constant up to 1974, then increased up to 1982, where the rate was 1.8 times higher than in 1968, and decreased thereafter. On the other hand, the quadruplet birth rate remained nearly constant up to 1968, was eightfold in 1975, then decreased until 1984 and suddenly increased to 8 per million births in 1985. The higher multiple birth rates since 1974 was attributed to the higher proportion of mothers treated with ovulation-inducing hormones in Japan. The stillbirth rates decreased to 2/5 for male twins and to 1/3 for female twins during the 25-year period from 1960, to 2/5 for triplets and to 1/5 for quadruplets during the 34-year period from 1951.
双胞胎出生率在1968年之前几乎保持不变，1974年有所下降，之后逐年逐渐上升。三胞胎出生率在1974年之前几乎保持不变，到1982年有所上升，该年的出生率比1968年高出1.8倍，此后下降。另一方面，四胞胎出生率在1968年之前几乎保持不变，1975年增至八倍，之后下降直至1984年，1985年突然增至每百万例出生8例。1974年以来较高的多胞胎出生率归因于日本接受促排卵激素治疗的母亲比例较高。从1960年起的25年里，男双胞胎的死产率降至五分之二，女双胞胎降至三分之一；从1951年起的34年里，三胞胎的死产率降至五分之二，四胞胎降至五分之一。
