Background Both pregnancy disorders and low gestational age (GA) are associated with an elevated risk of cerebral palsy (CP). As many pregnancy disorders are associated with preterm birth, it is unclear whether the increased risk of CP in preterm children can be attributed to the pregnancy disorder or the low GA.

Aim To disentangle the risk of CP according to GA and pregnancy disorders in children born preterm.

Method Norwegian, national cohort study with linkage of the Medical Birth Registry of Norway to the Statistics Norway and the National Insurance Scheme. All births from 1967 to 2001 were followed through 2005, and 1,499,705 individuals were included in the cohort.

Results Placental abruption, chorioamnionitis, placenta previa, multiple birth, prolonged rupture of membranes, cervical conisation, unspecified bleeding and pre-eclampsia were associated with an increased risk of CP. The risk of CP increased with decreasing GA (23–27 wks RR 83.3 [95% CI, 69.8–99.4], 28–30 wks RR 49.5 [95% CI, 43.2–56.6], 31–33 wks RR 17.4 [95% CI, 15.3–19.7], 34–36 wks RR 3.3 [95% CI, 2.9–3.8]). The association between GA and CP was not substantially weakened after adjustment for pregnancy disorders.

Conclusion Although several pregnancy disorders were associated with an increased risk of CP, low GA appeared to be a more important risk factor for CP in preterm children.