Authors:
Blair E, Watson L.
Authors notes:
Developmental Medicine and Child Neurology. 2016;58:76-81.
Keywords:
cerebral palsy, pregnancy induced hypertension, gestational age
Abstract:
Aim: Pregnancy-induced hypertension/pre-eclampsia (PIH/PE) is associated with cerebral palsy (CP) in term births but if sufficiently severe to necessitate preterm delivery predicts a lower risk of CP than observed in gestational peers.
We investigated whether this apparent 'protection' was attributable to inappropriately chosen comparison groups and/or an increased risk of perinatal death.
Method: Perinatal information was collected from medical records of children with CP, individually matched neonatal survivors without CP, and representative samples of perinatal deaths of Western Australian birth cohorts from 1980 to 1995.
Compared with these data, the sensitivity of statutorily collected PIH/PE data was assessed for each outcome group.
Using these sensitivities, the estimated risks of death and CP in births to all women with and without PIH/PE were compared.
Results: Sensitivity of statutory PIH/PE data decreased with increasingly poor outcome.
Reconstructed cohorts showed that PIH/PE increased the risks both of CP and of perinatal death in births at lower gestations except in births <27 weeks, where the risk of perinatal death only increased greatly.
Interpretation: PIH/PE does not protect against poor outcome at any gestational age.
Previously reported protective effects originate from inappropriate control for gestational age and not from higher gestation-specific perinatal mortality.
What this paper adds: PIH does not protect the fetus from death or CP, whatever the duration of the pregnancy.
Causal inferences about factors that may exert their effect by curtailing gestational duration should not be drawn from studies controlling for gestational duration.
PIH/PE is a relatively benign cause of preterm delivery with respect to risks of death and CP.
Reconstructing cohorts from case-control studies of rare outcomes may overcome practical limitations associated with collecting accurate data on total population samples.
Death is a competing outcome of considerable significance in very preterm births and should not be ignored in epidemiological studies.