A characteristic change in infant mortality rate decrease in Japan.

Changes in infant mortality rate (IM) in Japan were observed over a 41-year period, since the end of the Second World War (1947-1987). Both neonatal mortality rate (NM) and infant mortality rate excluding neonatal deaths (IEN) were measured. It was observed that IM had considerably decreased during the observation period. A decrease of IEN contributed greatly to this fall till the 1960s and less so since the 1970s. The slope of the decrease of NM became steeper after entering the 1980s compared with that of IEN, and this contributed to the decrease of IM in this period. In order to analyse this phenomenon, detailed observations were made of the causes of death. On studying three of the major causes of infant deaths in Japan (congenital anomalies, birth trauma and perinatal asphyxia, and injuries and poisoning) it was found that there was only a small annual difference in the number of deaths due to congenital anomalies compared with the much greater difference seen with the other two causes; therefore, improvement of mortality rate by congenital anomalies seemed difficult because the efficacy of improvement of medical treatment and care are already approaching their limits. For a further reduction of IM in the future, improvement of perinatal care and prevention of injuries are considered to be essential.