[An analysis on a relationship between perinatal mortality and live births of low birthweight, in Kumamoto Prefecture, 1968-1994].

The aims of this investigation were to describe the relationship between perinatal mortality rates and the proportions of live births among low birth weight (LBW) infants from 1968 to 1994, and to determine risk factors in infants of low birth weight. Using vital statistics from 1968 to 1994 of the Japanese government and the Kumamoto Prefecture and Maternal and Child Health Statistics of Japan from 1968 to 1995, perinatal deaths and live births of infants of low birth weight were studied according to national statistics criteria. In Japanese and Kumamoto Prefecture, there was an association between perinatal deaths and live births of LBW. The significant decline of perinatal mortality rates from 1968 to 1976, of which the fetal death ratio at 28 weeks and over mostly declined, was closely related to the decline of live births of LBW. In this period, the improvement of socioeconomic conditions and the comprehensive health care provided by the government contributed in improving perinatal mortality rates. From 1977 to 1988, the annual variation of Kumamoto was different from that of all Japan. Both perinatal mortality rates continued to decline due to a general decrease in early neonatal mortality rates. The number of Live births of LBW infants in Kumamoto prefecture increased in 1977 and once again started to decline in 1982. In 1977, the insufficient maternal-child health care and the increase of female workers contributed to increasing rates of live births of LBW. Advances in neonatal medicine contributed to the increase in survival rates of infants of LBW. Although, after 1982, the improvement of maternal-child health care and the perinatal care system contributed to the declining rates of live births of LBW. On the other hand, those rates in all Japan continued to gradually increase from 1977 to 1988. After 1989, perinatal mortality rates continued to decline, and live births of LBW continued to increase in both Kumamoto prefecture and all Japan. These results were contrary to the above results from 1968 to 1976. It was considered that medical advances in the care of pregnant women and neonates increased survival rates of the LBW. In future, the perinatal mortality rates will appear to approach a minimum constant, that is, a minimum of fetal death rates. It is important to reduce the number of LBW infants, particularly birthweight of 2000 g-2499 g, with maternal-child health care.