[Regional differences in perinatal mortality rates in Japan--an investigation based on vital statistics].

OBJECTIVE This study investigated whether regional differences in perinatal mortality rates are related to distances to medical resources for perinatal care, such as the Neonatal Intensive Care Unit (NICU). METHODS Using the census for Japan in 2000, all municipalities in Japan were classified into four groups based on population size: municipalities of 1,000,000 people or more (Group 1), municipalities between 350,000 and 1,000,000 people (Group 2), municipalities between 10,000 and 350,000 people (Group 3), and municipalities of less than 10,000 people (Group 4). Then, using the vital statistics, perinatal mortality rates for all groups were calculated. In addition, setting the perinatal mortality rate in Group 1 as a referent, we calculated the differences in the rates to detect regional differences in perinatal mortality in Japan. Finally, we compared the distances between the municipality center and the closest NICU among the four groups by one-way ANOVA. RESULTS The perinatal mortality rates of Groups 1, 2, 3 and 4 were 5.38, 5.58, 5.88 and 6.31, respectively. The perinatal mortality rate ratios (95%CI) were 1.04 (0.96-1.12), 1.09 (1.03-1.16), and 1.17 (1.05-1.31), respectively. The perinatal mortality rate differences (95%CI) were 0.20 (-0.24-0.64), 0.50 (0.15-0.84), and 0.93 (0.23-1.62), respectively. The distances (95%CI) between the center of the municipalities and the closest NICU for Groups 1, 2, 3 and 4 were 2.61 (1.56-3.66) km, 4.23 (2.74-5.72) km, 20.79 (17.68-23.90) km and 38.07 (31.65-44.48) km, respectively. All of the differences among the groups were significant (p < 0.001), except for the difference between Group 1 and Group 2. CONCLUSION There are regional differences in perinatal mortality rates in Japan. This study suggests that the difference is associated with the uneven distribution of NICUs.