Cerebral palsy is the most common physical disability among children, with about two per 1000 live-born infants being diagnosed with the disorder. In most children with cerebral palsy, the disability is caused by damage to the immature brain during pregnancy or birth that results in problems with movement.
Denmark and Norway have low income inequality and free access to education and offer high-quality antenatal care to pregnant women free of charge. Nevertheless, in our study recently published in the International Journal of Epidemiology, we found that the risk of having a child with cerebral palsy in these two countries varies by the parents’ educational level, and this educational gradient has been surprisingly stable over time.
In our study, we aimed to assess whether the risk of having a child with cerebral palsy varied by different measures of parental socioeconomic status in Denmark and Norway. We found a strong educational gradient in the risk of having a child with cerebral palsy in both countries – the higher the education of the parents, the lower the risk. There was a one-third reduction in risk among those with a Bachelor or higher degree compared with parents with only primary or lower secondary education. Decreased risks of the same magnitude were found independently for both mothers and fathers, and these trends were stable over the past four decades, despite a large increase in the proportion of parents with higher education, especially among women.
The Nordic countries are known for their redistributive tax system and social policies aimed at reducing socioeconomic differences. The Nordic model has been successful in many respects – for example, Denmark and Norway rank as two of the OECD countries with the lowest income inequality. However, paradoxically, the social inequality in adverse health outcomes is larger than in many other European countries, and increasing.
In our study, we found no association between household income and the risk of having a child with cerebral palsy, when adjusting for parental education and age. Among parents-to-be in the Nordic setting, income may be a poorer marker of socioeconomic status – income has been more responsive to social policy, and parents are early in their careers when they have children. In addition, a higher income does not necessarily result in healthier behaviour.
A recent study reported a decreasing prevalence of cerebral palsy in Norway since 1999. The same has been found in a multicenter study in Europe. This positive trend is believed to be due to improvements in obstetric and neonatal care. Still, in a majority of children with cerebral palsy, the cause is unknown. It may be due to either genetic or environmental factors in pregnancy that cause damage to the brain before birth or increase the infant’s susceptibility to brain damage during or shortly after birth. It is important to continue research to identify causal factors for cerebral palsy in these children.
Our study suggests that risk factors that differ by socioeconomic status – such as maternal overweight, smoking, poor diet, maternal infections, paracetamol use and chronic disease – may play a role, and that there could be room for further prevention. Maternal overweight, smoking, genitourinary infections and paracetamol use have been linked to increased risk of cerebral palsy, while chronic disease and dietary factors have been less often investigated.
We also hypothesise that recurrence of cerebral palsy within families could partly explain our results: if cerebral palsy in parents affects their chance of undertaking higher education and increases the risk of having a child with cerebral palsy. We were not able to assess these potential underlying mechanisms in our study, but we hope to answer some of these questions in ongoing studies.
Forthun I, Strandberg-Larsen K, Wilcox AJ, et al. Parental socioeconomic status and risk of cerebral palsy in the child: evidence from two Nordic population-based cohorts. International Journal of Epidemiology, dyy139, https://doi.org/10.1093/ije/dyy139.
Ingeborg Forthun is an economist and PhD student at the Department of Global Public Health and Primary Care, University of Bergen, Norway.