Imaizumi Y
Hum Hered. 1982;32(2):114-20. doi: 10.1159/000153269.
The effects of paternal and maternal ages, gestational age and the socioeconomic factor of occupation on the sex ratio of triplet individuals were analysed using data on 4,290 triplet individuals which occurred in Japan during the period from 1955 to 1967 and in 1974. The sex ratios among live births and fetal deaths slightly decreased with time. The decline of the sex ratio was related to the decline of age-specific fertility in older mothers. The mean sex ratio was 0.479 during the period. The sex ratio is not high but similar to those of Europe and the USA. The sex ratio was lower in triplets than in twins or the general population. It seems that predominant male triplets may be selectively aborted in early gestational age compared with that of twins or the general population.
利用1955年至1967年以及1974年期间日本出现的4290例三胞胎个体的数据，分析了父母年龄、孕周和职业社会经济因素对三胞胎个体性别比的影响。活产和死胎中的性别比随时间略有下降。性别比的下降与高龄母亲年龄别生育率的下降有关。在此期间，平均性别比为0.479。该性别比并不高，但与欧洲和美国的相似。三胞胎的性别比比双胞胎或一般人群的低。与双胞胎或一般人群相比，似乎男性占主导的三胞胎在孕早期可能会被选择性流产。
