In our previous study we reported that the secular change of the mean birth weight (MBW) of Okinawa was different from that of Japan as a whole, that is, the MBW of Okinawa was lower, but the annual increase rate of the MBW of Okinawa was larger than that of Japan as a whole. Through analyses using birth records of several obstetric facilities in Naha, we concluded that this phenomenon must be due to the remarkable improvement of the socioeconomical environment of Okinawa.
In this report we analyzed secular changes of mean birth weight (MBW) and mean gestational day (MGD) of 15, 847 singleton babies born at an obstetric clinic in the city of Naha for the 33 years from 1955 to 1987. To avoid fluctuations of annual changes in MBW and MGD caused by a small number of babies born in a single year, we also used the moving average of three years. In analyzing birth weight we stratified birth weight by sex, parity and the number of gestational weeks. It is considered that birth weight stratified by the number of gestational weeks reflects the intrauterine growth rate of infants.
According to our results, both the MBW of infants with 40 gestational weeks, which reflects the intrauterine growth rate, and the MGD increased during the period from the 1950s to the early 1970s in this clinic. On the basis of these results we concluded that the increase of birth weight in this clinic until the early 1970s was due to increases in both the intrauterine growth rate and the gestational period.
Our results also show that the mean height of mothers who delivered at this clinic also increased, which might reflect the development of the socioeconomical environment during their childhood. During the period when MBW increased, the economic growth rate of Okinawa was higher than that of other prefectures.
From these results we concluded that the MBW can be used as a community health indicator reflecting the total health condition in a given community.
