Maternal weight gain during pregnancy has been consistently associated with infant birth weight and pregnancy outcome. Our purpose was to determine the relationship between maternal weight gain pattern and birth weight. Consequently, maternal weight gain is monitored carefully and is encouraged during prenatal care in order to improve pregnancy outcome. Our study group included both 424 uncomplicated women and infant delivered at the Yeungnam University Hospital between 1993-1996. All recorded prenatal weight gain measurements were used to estimate maternal trimester weight gain, pattern of gain (based on low versus not-low gain at each trimester), and total gain at delivery. Multiple linear regression analysis was used to assess the relationship between these weight gain measurements and fetal birth weight. Each kilogram of maternal gain in the first, second, and third trimesters was associated with statistically related to the increase in fetal birth weight by 31.3, 19.0, and 24.5g, respectively. When compaired with the pattern of gain that was not low in any trimester, patterns with low gain in the first trimesters were associated with significant decreases in birth weight, but no important change in birth weight was seen for the group whose gains were not low in the first trimester. The results suggest that specific patterns of maternal weight gain, particularly weight gain during the first trimester, are related to fetal birth weight.