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Study: Increased Cerebral Palsy Risk Not Related to Infertility

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For some time, doctors have linked IVF procedures to an increased risk of cerebral palsy, but the reason behind this puzzling statistic has not been fully understood. Now, a new study provides evidence that the underlying infertility of the parents is not to blame.

Published online in the journal Human Reproduction, the study explored the relationship between the time it took parents to conceive and the number of cerebral palsy diagnoses. Cerebral palsy is neurological disorder that can develop during fetal growth or can result from brain injury during or after delivery. It affects body movement and muscle coordination, and can also cause difficulty speaking or performing precise motions.

The study found that out of 90,000 Danish children born between 1997 and 2003, only 165 were diagnosed with cerebral palsy, giving a rate of one out of every 545 children. However, the researchers found a much higher rate of cerebral palsy in children born after IVF or intracytoplasmic sperm injection (ICSI). In this group, one out of every 176 children was diagnosed with cerebral palsy.

While the relationship between IVF and cerebral palsy is not new, this study sought to explain its cause by looking to the parents’ underlying fertility. The study operated under the belief that parents who achieved pregnancy the quickest were the most fertile. The children were grouped according to how long it took their parents to conceive them, and results indicated that the time to conception had no bearing on the likelihood of developing cerebral palsy. There was no relationship between cerebral palsy and the time it took parents to conceive spontaneously, even in children of parents who tried for a year or more before conceiving.

“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,” said lead researcher Jin Liang Zhu, PhD, in a news release. “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.”

So what can account for the increased risk of cerebral palsy in children born through IVF? One of the possible reasons could be the increased rate of multiple births. The risk of cerebral palsy has been known to increase for multiple births of twins and triplets, especially if one of the multiples died. The researchers noted that children born through single embryo transfer IVF did appear to have lower rates of cerebral palsy.

Another possible cause for greater rates of cerebral palsy in IVF and ICSI births could be premature births, which also can be associated with twins, triplets, or higher multiples. Babies born prematurely with low birth weights are also at higher risk of developing cerebral palsy.

A previous Swedish study supports the link between IVF and increased rates of cerebral palsy. This 2005 study, which used a larger sample, concluded that the higher rate was “due to the high multiple pregnancy rate and prematurity.”

It is important to note that the risk for having a child born with cerebral palsy after IVF or ICSI is still low, at about one out of 176 children. And according to Professor Karl Nygren, one of the authors of the Swedish study, the rates of cerebral palsy after IVF may be decreasing, especially when certain precautions are taken during IVF.

"It seems to us that the previously noted increased risk of cerebral palsy after IVF is certainly decreasing and may actually have disappeared in recent years in countries that only transfer a single embryo at one time. This is good news,” he said in a news release.