title: [The comparative studies of the birth rates of opposite-sex twins between urban and rural areas in China].
abstract: The birth records of twins in 1989 in China were used to analyze the effects of difference between urban and rural areas on the birth rate of opposite-sex twin (OSTBR) at different maternal childbearing age. The results show that the urban and rural populations have the similar changing model of OSTBR with maternal childbearing age, the difference between urban and rural areas has an apparent influence on the OSTBR. The OSTBR in urban areas is commonly higher than that in rural areas, but the degree of the influence is related with maternal childbearing age.
authors.affiliation: The Department of Biology, Huanggang Normal College, Huanggang 438000, China. jpgan@sina.com
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Gan