Background
Preterm infants have an increased risk of neurodevelopmental disorders. We established a direct quantitative comparison of the association between the degree of prematurity and three different neurodevelopmental disorders.

Methods
In this cohort study, we combined data from 995,498 children in the Danish Medical Birth Register, from birth years 1997–2013, with information on cerebral palsy, epilepsy, and special educational needs. We estimated the gestational week-specific prevalence and risk for each of the disorders.

Results
The risk ratio of cerebral palsy at gestational weeks 21–24, compared to term birth, was more than ten times higher than for the two other disorders. The prevalence of epilepsy and special educational needs declined almost parallel, with 9.2% (4.6%–13.5%) and 12.5% (11.2%–13.7%), respectively, per week of gestation toward term birth. Cerebral palsy did not decline similarly: from gestational weeks 21–24 until week 29 the prevalence declined insignificantly by 0.6% (−11.1%–11.0%) per week; whereas from week 29 until term, the prevalence declined markedly by 36.7% (25.9%–45.9%) per week.

Conclusions
The prevalence and risk of cerebral palsy are affected differently by the degree of prematurity compared with epilepsy and special educational needs, possibly reflecting important differences in cerebral pathophysiology.