Imaizumi Y
National Institute of Population and Social Security Research, Ministry of Health and Welfare, Tokyo, Japan.
Acta Genet Med Gemellol (Roma). 1997;46(4):209-18. doi: 10.1017/s0001566000000441.
Trends of twinning rates were analyzed using vital statistics in Austria, Finland, Norway, Sweden, Canada, Australia, Hong Kong, Israel, Japan, and Singapore during the period from 1972 to 1996. The twinning rates increased significantly year by year in each country. During these periods, the twinning rate increased by twenty percent in Austria and Canada, and by sixty percent in Norway and Sweden. The twinning rate was 1.6 times higher in Sweden than in Hong Kong in 1972 and by eighty percent in Israel in 1995. Twinning rates were higher in European countries, Canada, and Australia than in Asia. The variations of the twinning rates among countries were not only due to biological factors, but also to assisted reproductive techniques. In Australia, the overall twinning rate was 1.3 times higher in the nuptial births (14.1 per 1000 births) than in the ex-nuptial births (10.7) during the period 1994-1996. As for maternal age, twinning rates in Sweden increased year by year for maternal age groups except the youngest and the oldest age groups. In Sweden, the rising twinning rate has been attributed to the higher proportion of mothers (for the 25-39 year old age groups) treated with ovulation-inducing hormones and attributed to in-vitro fertilization.
利用奥地利、芬兰、挪威、瑞典、加拿大、澳大利亚、中国香港、以色列、日本和新加坡1972年至1996年期间的人口动态统计数据，分析了双胞胎出生率的趋势。每个国家的双胞胎出生率均逐年显著上升。在此期间，奥地利和加拿大的双胞胎出生率增长了20%，挪威和瑞典则增长了60%。1972年瑞典的双胞胎出生率比中国香港高1.6倍，1995年以色列的双胞胎出生率比中国香港高80%。欧洲国家、加拿大和澳大利亚的双胞胎出生率高于亚洲国家。各国双胞胎出生率的差异不仅归因于生物学因素，还归因于辅助生殖技术。在澳大利亚，1994年至1996年期间，婚内生育的总体双胞胎出生率（每1000例出生中有14.1例）比非婚内生育（每1000例出生中有10.7例）高1.3倍。至于产妇年龄，瑞典除最年轻和最年长年龄组外，其他年龄组的双胞胎出生率逐年上升。在瑞典，双胞胎出生率上升归因于（25至39岁年龄组）接受促排卵激素治疗的母亲比例较高以及体外受精。
