Changes in the Distribution of Live Birth Weight in Japan

The purpose of the present study was to investigate the annual changes of coefficient variations of live birth weight and proportion of live birth weight from 1969 to 1981 in Japan, to clarify annual changes in the distribution of live birth weight. These analyses were done using vital statistics compiled by the Japanese government.The coefficient variations of live birth weight have declined annually from 1969 to 1976 and then increased slightly in the following years.The proportion of newborns with live birth weight less than 1.0kg decreased from 1969 to 1974 and then increased somewhat in the following years.The proportion of newborns with live birth weight less than 1.5kg, less than 2.0kg and less than 2.5kg decreased from 1969 to 1976 and then increased somewhat in the following years. Conversely, the proportion of newborns with live birth weight more than 4.0kg increased from 1969 to 1976 and decreased in the years following.The coefficient variations of live birth weight were affected by the proportion of low birth weight infants.