Gan Jian-Ping, Wu Zhong-Hua, Tu Zhi-Ming, Zheng Jian
The College of Life Science, Huanggang Normal University, Hubei, People's Republic of China.
Twin Res Hum Genet. 2007 Aug;10(4):633-7. doi: 10.1375/twin.10.4.633.
Based on the birth record data from the National Vital Statistics in the 1990 Census of China, the present study analyzed the differences between urban and rural areas on monozygotic (MZ) and dizygotic (DZ) twin rates by maternal age in 1989. The twins by zygosity were calculated with Weinberg's differential method. Results show that the MZ and DZ twinning rates in China were associated with maternal age and that there were substantial differences between urban and rural areas. The MZ twinning rates in urban and rural areas were 2.36 pairs and 2.11 pairs per 1000 deliveries respectively, significantly lower than that in most studied populations. Furthermore, our analysis indicated that MZ twinning rates remained relatively constant for mothers under the age group of 36 to 38 years, but rose over this age group in both areas, albeit with a different slope. The DZ twinning rates were strikingly affected by maternal age, but the age for peak DZ rates was found within the age group of 33 to 35 years. In all maternal age groups except for 24 to 26 years, the DZ twinning rates in urban areas were higher than in rural areas. It remains unclear as to why the DZ twinning rates reversed to reach higher values within the older maternal age groups in China, but it is almost certain that the high twinning rates had nothing to do with in vitro fertilization.
基于1990年中国人口普查中的国家生命统计出生记录数据，本研究分析了1989年按母亲年龄划分的城乡单卵双胞胎（MZ）和双卵双胞胎（DZ）发生率的差异。通过温伯格差分法计算不同合子性的双胞胎发生率。结果表明，中国的MZ和DZ双胞胎发生率与母亲年龄有关，城乡之间存在显著差异。城乡地区的MZ双胞胎发生率分别为每1000例分娩2.36对和2.11对，显著低于大多数研究人群。此外，我们的分析表明，36至38岁以下母亲的MZ双胞胎发生率相对保持稳定，但在这两个地区该年龄组以上发生率均有所上升，尽管斜率不同。DZ双胞胎发生率受母亲年龄的显著影响，但DZ发生率的峰值出现在33至35岁年龄组内。除24至26岁年龄组外，所有母亲年龄组中，城市地区的DZ双胞胎发生率均高于农村地区。目前尚不清楚为何中国年龄较大的母亲年龄组中DZ双胞胎发生率会反转至更高水平，但几乎可以肯定的是，高双胞胎发生率与体外受精无关。
