title: Why is there a modifying effect of gestational age on risk factors for cerebral palsy?
abstract: OBJECTIVE
  To investigate risk factors for cerebral palsy in relation to gestational age.
  
  
  METHODS
  Three case-control studies within a geographically defined cohort.
  
  
  METHODS
  The former Oxfordshire Health Authority.
  
  
  METHODS
  A total of 235 singleton children with cerebral palsy not of postnatal origin, born between 1984 and 1993, identified from the Oxford Register of Early Childhood Impairment; 646 controls matched for gestation in three bands: <or=32 weeks; 33-36 weeks; >or=37 weeks.
  
  
  RESULTS
  Markers of intrapartum hypoxia and infection were associated with an increased risk of cerebral palsy in term and preterm infants. The odds ratio (OR) for hypoxia was 12.2 (95% confidence interval 1.2 to 119) at <or=32 weeks and 146 (7.4 to 3651) at >or=37 weeks. Corresponding ORs for neonatal sepsis were 3.1 (1.8 to 5.4) and 10.6 (2.1 to 51.9). In contrast, pre-eclampsia carried an increased risk of cerebral palsy at >or=37 weeks (OR 5.1 (2.2 to 12.0)) but a decreased risk at <or=32 weeks (OR 0.4 (0.2 to 1.0)). However, all infants <or=32 weeks with maternal pre-eclampsia were delivered electively, and their risk of cerebral palsy was no lower than that of other electively delivered <or=32 week infants (OR 0.9 (0.3 to 2.7)). Nearly 60% of <or=32 week controls were delivered after spontaneous preterm labour, itself an abnormal event.
  
  
  CONCLUSIONS
  Inflammatory processes, including pre-eclampsia, are important in the aetiology of cerebral palsy. The apparent reduced risk of cerebral palsy associated with pre-eclampsia in very preterm infants is driven by the characteristics of the gestation matched control group. Use of the term "protective" in this context should be abandoned.
authors.affiliation: National Perinatal Epidemiology Unit and The Women's Centre, John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DU, UK. Catherine.Greenwood@orh.nhs.uk
authors.forename: C
authors.initials: C
authors.lastname: Greenwood
authors.forename: P
authors.initials: P
authors.lastname: Yudkin
authors.forename: S
authors.initials: S
authors.lastname: Sellers
authors.forename: L
authors.initials: L
authors.lastname: Impey
authors.forename: P
authors.initials: P
authors.lastname: Doyle
mesh_terms: D015415:Biomarkers / Q000032:analysis; D016022:Case-Control Studies; D002547:Cerebral Palsy / Q000209:etiology*; D036861:Delivery, Obstetric / Q000379:methods; D005260:Female; D005311:Fetal Hypoxia / Q000150:complications; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases / Q000503:physiopathology; D007236:Infant, Small for Gestational Age / Q000502:physiology; D007744:Obstetric Labor Complications / Q000503:physiopathology; D011225:Pre-Eclampsia / Q000503:physiopathology; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000503:physiopathology; D012307:Risk Factors; D018805:Sepsis / Q000150:complications
chemical_list: D015415:Biomarkers
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