Neonatal seizures: incidence, onset, and etiology by gestational age.

OBJECTIVE: To examine the influence of gestational age on seizures in the neonatal intensive care unit.

STUDY DESIGN: A cohort of 4165 neonates admitted to a university intensive care unit between 1986 and 1995. The incidence, time of onset, and etiology of neonatal seizures in the cohort were distributed by gestational age. Logistic regression and t test were used to examine the relationship between gestational age and seizures in the neonatal intensive care unit.

RESULTS: Seizures occurred in 356 (8.6%) infants. The seizure rate was parabolically related to gestational age, such that infants at 30 to 36 weeks' gestation had a 4.8% rate compared with 11.9% and 14.1% rates for infants < 30 and > 36 weeks, respectively (p < 0.001). Seizures manifested earlier in infants < 30 weeks (2.3 +/- 5.6 days of life) and > 36 weeks (3.7 +/- 8.7 days) gestational age compared with neonates 30 to 36 weeks (10.4 +/- 14.5 days) (p < 0.001). Intraventricular hemorrhage was the principal etiology underlying the higher seizure rate for infants < 30 weeks (p < 0.001). Hypoxic-ischemic encephalopathy and congenital malformations were primary factors for infants > 36 weeks (p < 0.01). Nervous system infections were evenly distributed across gestational age.

CONCLUSION: Gestational age exerts a considerable influence on the incidence, onset, and etiology of neonatal seizures.