母亲年龄对中国双生子出生率的影响

选用全国人口普查时登报的 1 989年 1月 1日至 1 2月 31日期间中国育龄妇女 ( 1 5— 49岁 )的生产记录 ,用 Weinberg差别法进行双生子卵性分类 ,分析了中国总体、DZ和 MZ双生子出生率与母亲年龄之间的关系以及双生子的出生性别比。结果表明 ,中国总体、 DZ和 MZ双生子的出生率分别为 0 .787± 0 .0 0 2 % ,0 .573± 0 .0 0 2 %和 0 .2 1 4± 0 .0 0 1 % ,DZ双生子出生率在 33岁前随母亲年龄增高单调上升 ,随后下降 ,但在 46岁后又随龄上升 ,MZ双生子出生率在 34岁前相对恒定 ,随后随龄上升。中国双生子出生性别比显著性低于同期群体出生性别比 ,1 5— 1 9岁和 45— 49岁年龄组出生的双生子性别比低于其它年龄组出生的双生子性别比 ,1 5— 1 9岁和 45— 49岁年龄组出生的双生子性别比较低可能是较低的 MZ双生子出生性别比造成的。

THE INFLUENCE OF MATERNAL AGES ON THE BIRTH RATES OF TWINS IN CHINA

The birth records of Chinese child-bearing age women ( aged 15- 49) available at the census in 1989 from January 1st to December 31st are used to analyse the relationship between the birth rates of total, DZ and MZ twins and the maternal ages and the twins sex ratios in China by means of Winberg 's difference method to compute the zygosity of the twins. The results show that the birth rates of total, DZ and MZ twins in China are 0. 787 ± 0. 002% , 0. 573± 0. 002% and 0. 214± 0. 001% respectively. The birth rate of DZ twins increase monotonously with the increasing maternal age before 33, and then decrease, but increase again after 46. The birth rate of MZ twins keeps relatively stable before 34, and then increase with maternal age. The twins sex ratio is lower than that of the same population significantly in China, and the twins sex ratios at the age groups of 15- 19 and 45- 49 which are possibly caused by the lower MZ twins sex ratios are lower than that at any other age groups.