Spastic cerebral palsy: changes in birthweight and gestational age.

The birthweight and gestational age frequency distributions for spastic cerebral palsy (CP) cases and their controls were obtained from the Western Australian CP register. Following the introduction of neonatal intensive care, spastic CP rates have fallen amongst heavier (greater than or equal to 2500 g) infants and remained steady or risen amongst low birthweight (LBW: less than 2500 g) infants. The expected bimodality of both the birthweight and gestational age distributions for spastic diplegia cases was obvious in these data. Marked peaks occurred at 1500 g and 31 weeks and 3000 g and 39 weeks. The numbers of heavier, term diplegics fell between 1961-1965 and 1971-1975, and thus there were proportionally more preterm LBW diplegics more recently. The reasons for the fall in the heavier diplegics need investigation. Spastic hemiplegic and quadriplegic cases were more like the controls but with distributions skewed to the left. More of these individuals were more recently small for gestational age (SGA: less than 2500 g and over 37 weeks gestation). This highlights the importance of intrauterine damage in these two groups of spastic CP individuals.