目標：分析1982、1987、1992、及1997年臺灣地區活產嬰兒之出生體重與妊娠週數分佈。方法：在經過合理妊娠週數與出生體重之篩選後，本研究計算各年度和嬰兒出生特徵別出生體重與妊娠週數之平均值與標準差，以及年度別低出生體重(＜2500公克)與早產(＜37週)之百分比；此外，也分析歷年可能影響出生體重或妊娠週數之嬰兒或母親人口學特徵，並繪製1982與1997年兩個年度的妊娠週數別出生體重曲線。結果：臺灣地區嬰兒於1982-1997年間平均出生體重下降了3.2%(105公克)，低出生體重百分比則上升了33.3%；妊娠週數平均值也減少了2.3%(0.9週)，早產盛行率則上升了230%。多胞胎嬰兒平均體重與妊娠週數下降之百分比在各分層中均屬最高，分別為16.8%與8.5%。嬰兒性別比例與胎次分佈在研究期間無明顯變化，但35歲以上母親與雙/多胞胎之分率則分別增加了3.8倍與13倍。妊娠週數少於34週早產嬰兒的平均體重於1997年的數值明顯低於1982年的數值。結論：研究期間出生體重與妊娠週數平均值下降可能與出生登記資料的完整性以及醫療照護品質逐年提昇有關；出生體重下降也可能與雙或多胞胎佔整體活產比率的增加，以及與有愈來愈多34週前的低出生體重早產兒能夠存活有關。

　　　　　Objectives: To analyze the calendar-year specific distributions of birth weight and gestational age among live births in Taiwan for the years 1982, 1987, 1992, and 1997. Methods: After excluding implausible gestational age and birth weight, we calculated calendar or birth characteristics specific means and standard deviations of gestational age and birth weight. We also estimated the calendar-year specific rates of low birth infants (＜2500 grams) and pre-term birth (＜37 completed gestational weeks). Certain infant and maternal characteristics suspected of being associated with birth weight or gestational age were also calculated. We finally draw a gestation specific birth weight curve for the years 1982 and 1997, respectively. Results: The mean birth weight decreased by 3.2% (105 grams) between 1982 and 1997, and the rate of low birth weight of infant increased by 33.3%. The gestational weeks also reduced by 2.3% (0.9 weeks) and the rate of pre-term birth increased dramatically by 230% (2.6%-6.3%). Triplets or higher births showed the most reduction in both birth weight (16.8%) and gestational age (8.5%). Between the study period, the sex ratio and birth order distribution showed little variation whereas the proportion of mothers aged 35 or more and that of multiple births increased substantially by 3.8 and 13 times, respectively. Conclusions: The reduction of birth weight and gestation during the study period is possibly related to improvement in both health care services and completeness of birth registration. An increase in multiple births and a higher survival rate of very pre-term birth (＜34 weeks) might also contribute to the reduction of birth weight in recent years.