Incidence patterns of cerebral palsy in Shiga Prefecture, Japan, 1977-1991.

The prevalence of cerebral palsy (CP) in 6-year-old children in Shiga Prefecture, Japan, born between 1977 and 1991, was compared in three successive 5-year periods: period I (1977-1981), period II (1982-1986) and period III (1987-1991). Data on the accumulated age-specific prevalence of CP were collected and analyzed. During the study period, 242293 children entered elementary school, and 325 cases (194 boys, 131 girls) of CP were ascertained in Shiga Prefecture. The overall prevalence of CP per 1000 6-year-old children was 1.34. The prevalence of CP for 6-year-old children increased from period II to period III, although it did not vary from period I to period II. The proportion of low birth weight (LBW) infants and preterm infants among those with CP increased with time during the study periods. The prevalence of CP in infants born at term and with birth weight > or =2500 g did not vary over the study period. The prevalence of CP in preterm and LBW infants, especially in infants with gestational age<32 weeks and birth weight<1500 g, increased from period II to period III, while the prevalence did not increase from period I to period II. Multiple births and use of mechanical ventilation increased from period II to period III. The changes in the prevalence of CP in Shiga Prefecture may have been due to increased survival of preterm and LBW infants in period II owing to better obstetric and neonatal care, and to further improvement in the survival of very small babies receiving intensive care, which increased the prevalence of CP in period III. Further improvement of perinatal care might decrease the incidence of CP in Shiga Prefecture in the future.