A changing pattern of cerebral palsy. Declining trend for incidence of cerebral palsy in the 20-year period 1970-89

Abstract

In a population-based study cerebral palsy (CP) was diagnosed in 110 cases (2.4 per 1000) among children live born with birth weight > or = 500 g (n = 45,976) during the 20-year-period 1970-89 (CP cases with a postneonatal etiology excluded). The CP-incidence showed a linear trend of decline from 2.8 per 1,000 in the first 5-year-cohort born 1970-74, to 2.0 per 1,000 in children born 1985-89 (p = 0.17). Birth weight specific CP-incidence showed a trend of decline in very low birth weight infants (500-1,499 g) and in infants > or = 2,500 g from the first 10-year-cohort born 1970-79 to the second born 1980-89. The same trend occurred for the incidence of spastic diplegia in total and in children born preterm. These trends of decline did not achieve statistical significance (p > 0.05). The CP-incidence was 36.7 and 11.3 times higher among infants with birth weight 500-1,499 g and 1,500-2,499 g respectively compared to infants > or = 2,500 g (p < 0.01). 15.9% of the decline in CP-incidence from the first to the second 10-year-cohort could be explained by a decreased low birth weight rate (500-2,499 g) in the population, from 4.2% 1970-79 to 3.8% 1980-89 (p < 0.05). The origin of CP was considered prenatal in 22 (20%), perinatal in 47 (42.7%), and undifferentiated in 41 (37.3%) of the cases. More CP-children born in the 10-year-period 1980-89 were treated with mechanical ventilation in the neonatal period (13/46; 28.3%) than those born in the 10-year-period 1970-79 (4/64; 6.3%) (p < 0.01). The neonatal mortality rate declined significantly from 7.2 per 1,000 in the first to 3.9 per 1,000 in the last 10-year-cohort respectively (p < 0.01). Birth weight-specific neonatal mortality rates declined more than 50% in all weight groups (p < 0.01). The results are contradictive to other investigations showing increased CP-incidence following improved survival rates in low birth weight infants, and may reflect a different pattern for development of perinatal care (organization, intensive care). The overall effect of mechanical ventilation may be improved survival and prevention of brain damage, though the percentage of ventilated CP-children increased. Preventing low birth weight should be a main strategy for preventing CP.