Babies conceived through in vitro fertilization (IVF) – informally known as test-tube babies – are significantly more likely than other newborns to suffer complications. It's not because of genetic defects, but rather because IVF procedures frequently produce twins, triplets or higher degrees of multiples. Multiples are more likely to be born prematurely, and thus to suffer complications afterward.
A new study led by Keith Barrington, chief of neonatology at Sainte-Justine University Hospital in Montreal, has measured how extreme the causation is: While IVF accounts for only 1 percent of Canadian births, 17 percent of babies admitted to the neonatal intensive care unit (NICU) where Barrington works were IVF babies. An American doctor confirmed that the numbers are similarly disproportionate in the United States. In his paper, published in the upcoming Journal of Pediatrics, Barrington advocates legal intervention to reduce the risk.
In IVF, eggs are fertilized with sperm in a laboratory. A few days later, when the fertilized eggs have developed into multi-cellular masses, one or more of these embryos are transferred into a woman's uterus. "In the latest U.S. report on mothers under 35 years, 10 percent had a single embryo transferred, and 90 percent had two or more," Barrington told Life's Little Mysteries, a sister site of LiveScience.
Women don't necessarily go into the procedure wanting to have multiples, but when more than one embryo is transferred, they are more likely to get pregnant at all. Compared to natural pregnancies, it's also much more likely they'll end up expecting twins or triplets. And this is what puts these babies at risk.
"For triplets, the rate of prematurity is very close to 100 percent. For twins it is about 70 percent," said Barrington.
Premature babies face grave health risks. "A substantial proportion and very likely the majority of infants admitted to a NICU (neonatal intensive care unit) are admitted because of complications relating to prematurity," Marc Fritz, chief of reproductive endocrinology and infertility at the University of North Carolina School of Medicine, explained.
The health problems faced by these premature newborns place a huge burden on Canada's national health care system. Barrington calculated that a mandatory one-embryo transfer policy would dramatically reduce neonatal intensive care with estimated annual savings of approximately $40 million.
Several European countries with nationalized health care have instituted the one-embryo policy already, and Quebec implemented the rule last year for mothers under 35. Since then, Barrington said, the number of twin pregnancies in Quebec resulting from IVF has gone from 30 percent to 3.8 percent, and there are no more triplets.
The United States does not have nationalized health care, and so IVF places no large burden on the government, or on insurance companies. "Costs are borne primarily by the patients themselves, because IVF is not covered by insurance in the large majority of states," Fritz said.
Costs aside, though, infant lives might still be saved by a one-embryo policy, Barrington argues. He says such a requirement in the U.S. could prevent the deaths of 700 premature twins and triplets a year, out of a total of about 41,000 IVF births.
But mothers for whom the chance of pregnancy is very low will likely suffer from a one-embryo law, Fritz cautioned.
"Whereas it is true that the number of multiple births resulting from IVF is significantly lower where such policies are in place, it also is true that success rates are significantly lower in those countries than they are in the U.S, where the maximum number of embryos transferred is governed by practice guidelines rather than by law," said Fritz.
Fritz believes medical research, rather than government policy, ought to address the problem. "Strict regulation certainly is one way to achieve the goal [of reducing the incidence of multiple births resulting from IVF], but one that would unfairly penalize many couples and preclude their being able to have children," he said.
"Much of research in the field is aimed squarely at finding methods for optimal embryo selection, so as to be able to reduce further the average number of embryos transferred without significantly decreasing the likelihood for achieving a successful pregnancy."
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Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.