There is now evidence that rates of cerebral palsy are higher among children born via in vitro fertilization (IVF). There has been speculation that the parents’ infertility could be a reason but this new study is the first that links the procedure to the condition.
Researchers at the University of Aarhus in Denmark showed that babies born by IVF were more than twice as likely to have cerebral palsy as those conceived naturally. They adjusted for factors like age of the mother, if she smoked, and whether the baby was premature or a twin. About one in 176 children born via IVF in the study had the condition, compared to the British average of about one in 400.
This cohort study followed pregnant women from 16 weeks of pregnancy to the birth of their baby. It looked at the risk of cerebral palsy and whether it was associated with the parents’ fertility history, i.e. was the risk greater for babies of parents who took longer to conceive or had IVF treatment. The research used data from women included in the Danish National Birth cohort whose pregnancy resulted in a live birth between 1997 and 2003. Cases of cerebral palsy were identified by linking the details of the babies to the Danish Cerebral Palsy Register, which includes all children with a diagnosis of cerebral palsy validated by a neuro-pediatrician in Denmark since 1995. There are approximately 170 new cases of cerebral palsy in Denmark every year.
Among the 90,203 children born, 165 were diagnosed with cerebral palsy (0.18%). Of these, 145 children had been among the 86,223 singleton births (0.17%), 18 were one of the 3,834 (0.47%) twins born and two were one of the 95 (2.11%) triplets born. The researchers found that there was no association between the time attempting to conceive and the risk of cerebral palsy.
Lead researcher Dr Jin Lieang Zhu, an epidemiologist and colleagues concluded that IVF was probably the underlying cause by looking at how rates of cerebral palsy changed depending on how long it took the mother to conceive naturally. This is considered a good measure of underlying fertility. They found no statistically significant difference in rates between those whose mothers took less than two months to conceive, and those who took more than a year. Difference came out between those who took over a year to conceive and those who only got pregnant with IVF. Researchers even from the small number of cases of cerebral palsy concluded that IVF “confers a risk of cerebral palsy”. Dr Zhu however stressed that the overall risk of having a child with cerebral palsy was still low. He also said that modern IVF techniques, such as only transferring one embryo to the womb, could eliminate the heightened risk altogether.
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 that this was not the case because, even for couples who took a year or longer to conceive, there was no statistically significant increased risk if they conceived spontaneously. More research is needed into why there might be an increased risk of cerebral palsy associated with IVF/ICSI, besides the pathway of multiple pregnancies and preterm births. It is also important to remember that IVF/ICSI techniques have developed and improved considerably since 2003, when the youngest children in our study were born.”
The study is published today in the journal Human Reproduction.
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