Allen G, Parisi P
US Public Health Service, Bethesda, Maryland.
Acta Genet Med Gemellol (Roma). 1990;39(3):317-28. doi: 10.1017/s0001566000005225.
The dizygotic twinning rate in Italy, adjusted for maternal age and parity, declined from 8.9/1000 in 1949-1953 to 6.0/1000 in 1978-81, but may have stabilized or recovered slightly in the early 1980s. The long decline was greatest in the oldest mothers, and the recent increase, if any, has been principally in first births and in women under 30. The monozygotic rate rose from 3.8/1000 in 1969-73 to 4.3/1000 in 1982-85, having been relatively stable prior to that period. No good explanation for these trends is apparent.
在意大利，经产妇年龄和胎次调整后的双卵双胎率从1949 - 1953年的8.9‰下降至1978 - 1981年的6.0‰，但在20世纪80年代初可能已趋于稳定或略有回升。长期下降在年龄最大的母亲中最为明显，而近期的增长（如果有的话）主要出现在头胎生育以及30岁以下的女性中。单卵双胎率从1969 - 1973年的3.8‰升至1982 - 1985年的4.3‰，在此之前相对稳定。目前尚无明显的合理解释来解释这些趋势。
