A new study suggests factors other than a couple's underlying fertility problems may explain an increased risk of cerebral palsy seen in children born following fertility treatment. Researchers at the University of Aarhus in Denmark who conducted the study emphasised the overall risk of cerebral palsy in children conceived through IVF or ICSI (intracytoplasmic sperm injection) remains very low - approximately 0.57 percent, or one in every 176 babies born.
In a study of more than 90,000 children from the Danish National Birth Cohort, Dr Jin Liang Zhu and colleagues compared rates of cerebral palsy in children conceived naturally, after different lengths of time taken for couples to conceive, with those conceived through IVF/ICSI. The length of time taken to conceive was used as a measure of a couple's fertility - in couples that struggle to conceive within a year, one or both partners may have an underlying fertility problem.
The researchers found the rates of cerebral palsy in children conceived after more than one year of trying and children conceived within two months of trying were not different. Children born through IVF/ICSI, however, had approximately double the risk of cerebral palsy compared with children conceived within two months of trying. This finding was observed even after adjusting for factors such as the mother's age and smoking status, and after adjusting for premature or multiple births, which are known to be more common in IVF pregnancies.
The researchers concluded underlying fertility problems did not account for the increased risk of cerebral palsy associated with IVF/ICSI. Other factors that might be contributing to the increased risk are unclear, but may include the procedure itself, or complications of multiple pregnancy.
Dr Zhu said: 'Our research enabled us to examine whether untreated subfertility, measured by time to pregnancy, might be the reason for the higher risk of cerebral palsy after IVF/ICSI. Our results showed this was not the case because, even for couples that took a year or longer to conceive, there was no statistically significant increased risk'.
'It is important to stress that the risks of cerebral palsy after IVF/ICSI are low. Out of more than 90,000 children in the Danish National Birth Cohort, born between 1997 and 2003, only 165 (0.18 percent) were diagnosed with cerebral palsy. Of the 3,000 children in this cohort born after IVF/ICSI, only 17 (0.57 percent) had cerebral palsy', he said.
Another recent study of over 2.6 million children in Sweden found the risk of cerebral palsy increased in multiple birth pregnancies rather than as a result of IVF itself. The Swedish researchers suggested that the practice of only transferring one embryo back into the mother during the IVF treatment rather than two or more, which has become common in recent years, might account for the reduction in cases of cerebral palsy that has been lately observed.
Cerebral palsy is a rare disease in the UK, affecting approximately two per 1,000 live births in the general population. Although the overall risk is low, given that more than 12,000 children are born through IVF every year in the UK, the issues 'deserve further research', according to Professor Richard Fleming from the Glasgow Centre for Reproductive Medicine, to determine how to reduce the risk of cerebral palsy.