中文摘要：

目的描述分析中国双生子出生体重变化趋势。方法使用中国双生子登记系统在中国8个省份收集的1995—2012年出生的双生子人群（共10827对），采用病例回顾方法分析出生体重各指标情况和变化趋势。结果调整性别、卵型、出生地区后，出生年份每推迟5年，双生子出生体重平均值降低O．01kg（P=0．041）。随着时间变化，双生子优势方出生体重、劣势方出生体重均不同程度地降低，出生体重相对差与出生体重不一致率在2007年以后有升高趋势。结论1995—2012年中国双生子出生体重呈下降趋势，出生体重不一致率逐渐上升。考虑到出生体重不一致与某些不良健康结局的风险存在关联，应对双生子出生体重不一致予以重视。

英文摘要：

Objective To understand the change trend of birth weight of twins in China from 1995 to 2012. Methods A total of 10 827 twins born between 1995 and 2012 registered in national twin registry system in 8 provinces in China were included in this study. A retrospective study was conducted to analyze the change trend of twin＇ s birth weight. Results Mean birth weight of twins decreased by 0.01 kg every five years after adjusting sex, ovum type and place of birth （P=0.041）. The birth weight decreased both in superior twin and in inferior twin over time. After 2007, the birth weight of superior twin decreased by 0.008 kg each year, while the birth weight of inferior twin decreased by 0.014 kg each year. Mean relative difference in birth weight and birth weight discordant rate decreased before 2002, then increased from the lowest point 8.16% and 16.20% to highest point 9.99% and 22.40% respectively. Conclusion The birth weight of twins in China decreased between 1995 and 2012, while the birth weight discordant rate increased, suggesting that close attention should be paid to the discordance of twin body weight to reduce the risk of adverse health outcome.