Study shows IVF babies at higher risk of heart defects

A new study conducted by the University of Gothenburg, Sweden has revealed that major heart defects are more common, but still rare, in babies conceived through certain fertility treatments, including in vitro fertilisation.

The research, which included medical records of more than seven million Nordic children, also supported evidence that I.V.F. is associated with a small but significant uptick in birth abnormalities.

“It’s an increased risk, but the absolute risk is very small,” Ulla-Britt Wennerholm, the senior author of the paper and a professor of obstetrics and gynaecology at the University of Gothenburg in Sweden.

“I think that’s a reassuring finding.”

The study focused on children born between 1984 and 2015 in Denmark, Sweden, Norway, and Finland as a result of a class of fertility treatments called assisted reproductive technology, the most common of which is I.V.F.

The risk of a major heart defect was about 36 per cent higher in this group than in children who were naturally conceived. But the defects were still uncommon: less than two per cent of infants conceived through A.R.T. were born with major heart defects.

The risk of heart defects didn’t change based on whether the parents underwent ICSI, a procedure in which sperm is injected into an egg, or IVF, which allows the sperm to penetrate the egg naturally in a lab dish.

It also did not make a difference whether the implanted embryos had been frozen for later use or the doctors implanted the embryos shortly after the eggs were fertilized in the lab.

The link between IVF and birth defects of all kinds, including those that affect the muscles, genitals, and gastrointestinal tract — has been well established in the scientific literature, said Jeffrey Kuller, a maternal-fetal medicine specialist at Duke Health in a report seen by BusinessDay.

The reason for that association isn’t clear, though.

One theory is that something about the IVF process — which involves extracting a woman’s eggs, fertilizing them in a lab, and then transferring the resulting embryo into the woman’s uterus — may be responsible.

Another theory, Kuller said, is that infertile parents have genetic differences that make their children more likely to have birth defects. For example, there is evidence that infertile men are more likely to have missing genetic material on the Y chromosome, which may be associated with some defects.

The high prevalence of twins and multiple births among women who undergo these fertility treatments may also contribute to the higher risk. Twins and multiples, however they were conceived, had the highest risk of heart defects, the study found.

Multiple births are more common with fertility treatments like IVF because doctors sometimes transfer more than one embryo to increase the odds of a successful pregnancy. Even single-embryo transfers are more likely to divide into twins than in a naturally conceived pregnancy.

But as the dangers of twin pregnancies have become clearer and implantation has become more successful, the practice has become less common.

In more than 80 per cent of procedures in 2020, just one embryo was transplanted, up from about 20 per cent in 2011, according to the Centers for Disease Control and Prevention.

Wennerholm said she hoped that more recent data would show a drop in heart defects as a result of that shift. “I think that’s an important message to clinicians and patients: You should go for a singular embryo transfer,” she said.