Rates of cerebral palsy among babies in Nordic countries born through in vitro fertilization (IVF) have fallen by more than half over the past two decades, due to fewer twin births from IVF, according to a new study.
A study in Denmark 15 years ago found a significantly increased risk of cerebral palsy in infants born through IVF. The absolute risk was small, but cerebral palsy was the greatest developmental birth defect risk associated with the infertility procedure.
"Multiple embryo transfer is still standard care in many countries," said study author Dr. Anne Lærke Spangmose of Rigshospitalet at Copenhagen University Hospital in Denmark. "Our findings emphasize that single embryo transfer and singleton births should be encouraged worldwide."
The new study analyzed data on nearly 112,000 babies born through IVF over 24 years in Denmark, Finland and Sweden. They were compared with nearly 5 million babies who were conceived naturally.
The overall rate of cerebral palsy during the study period fell from 12.5 cases per 1,000 live births in 1990-1993 to 3.4 per 1,000 in 2011-2014.
The rate dropped only slightly in the children conceived naturally — from 4.3 to 2.1 per 1,000. Among single babies born through IVF, the rate fell from 8.5 per 1,000 to 2.8 per 1,000.
However, the rate among IVF twins remained stable at 10.9 per 1,000, according to the study. The results were presented at the online annual meeting of the European Society of Human Reproduction and Embryology.
The findings provide strong evidence that reducing the number of twins born after IVF treatment has lowered the risk of cerebral palsy in IVF babies to a level comparable with those naturally conceived, said Lærke Spangmose.
She noted that over the past two decades there has been considerable reduction in twin birth rates after IVF treatment.
This is especially so in the Nordic countries, Lærke Spangmose said in a meeting news release. There, IVF twin rates have declined from almost 25% in the 1990s to less than 5% today, which isn't much higher than the 2% twin rate in naturally conceived pregnancies.