A study of 35,919 live neonates was conducted from 1976 to 1987 (excluding 1980) at a teaching hospital in Central Taiwan. Our goal was to determine the proportions of low birth weight (LBW) and very low birth weight (VLBW) and birth weight/birth length ratios by gestational week. The results showed that LBW and VLBW neonates were 6.3% and 1.1%, respectively. In LBW neonates groups, there was a rapid decline after the 33rd gestational week, then as low as 6.9% by the 38th gestational week. After the 28th gestational week, there was a rapid decline in VLBW proportion, then a further decline to 9.3% at the 32nd gestational week. Birth weight/birth length ratios were 2.94 and 6.25 at the 28th and 39th gestational weeks, respectively. There were no differences in birth weight/birth length ratios between male and female babies. Based on the above findings, we tried to set a norm from birth weight/birth length ratios by gestational week.