GEOGRAPHIC DIFFERENCES IN SEASONALITY OF PRETERM BIRTHS IN JAPAN

Based on vital statistics from 1979 to 1983, we used a time-series ana lysis using the Box-Jenkins model (ARIMA model) to compare the seasona lity of preterm births among 47 prefectures in Japan. We also evaluate d the relation between seasonality of preterm births and temperature. According to the Box-Jenkins analysis, a seasonal moving average was d etected for 44 prefectures. The seasonality of preterm births in gener al shows a bimodal pattern with two peaks, one in summer and one in wi nter. The most interesting result is that the peaks show a trend with geographic location; one peak is dominant in winter among the northern prefectures and the other peak is dominant in summer among the southe rn prefectures. Another important result is that the winter increase i n preterm births is negatively correlated with mean winter temperature (R = -0.424, p = 0.003); on the contrary, the summer increase in pret erm births is positively correlated with the average summer temperatur e (R = 0.549, p < 0.001). These results suggest that climate-associate d factors should be associated with the occurrence of preterm births i n Japan.