Frozen embryo transfers for IVF now outperform fresh transfers in terms of live birth rates, by almost 5%, thanks to better freezing and storage technologies.
Clinicians say this is especially promising news for cancer patients who wish to have children after chemotherapy.
Incremental yearly improvements in the techniques, technology and understanding of assisted reproductive technology led to a 28% overall live birth rate per embryo transfer in 2019, up from 22% in 2010.
In real terms, women who underwent IVF gave birth to 16,300 babies in Australia and New Zealand during 2019, according to the Australian and New Zealand Assisted Reproduction Database’s most recent report on assisted reproduction technology.
The report, which was released this week, found that the most notable improvements over the 10 years to 2019 were in thawed embryo transfers, where the embryo has been cryogenically frozen.
“In the last five years the live birth rate per fresh embryo transfer cycle increased from 23.9% to 25.5%, and the live birth rate per thaw embryo transfer cycle increased from 26.7% to 29.7%,” the authors said.
“The greater increase in live birth rates from thaw embryo transfer cycles could be explained by more freeze-all cycles being performed over the years.”
The increase was most significant for women older than 44, whose chance of a live birth is just 2% with a fresh cycle, but 9% with a thaw cycle.
Lead author Professor Georgina Chambers said one of the main reasons for the increased success of thaw cycles could be improved freezing processes.
“A lot of it is due to improvements in cryo-preservation methods, where we now use vitrification to snap freeze the embryo or the egg,” said the director of the National Perinatal Epidemiology and Statistics unit at the University of New South Wales.
“And that has proven to be more successful in terms of storing the egg or embryo, rather than older methods that tended to use a slow freezing method,” she told The Medical Republic.
“We also tend to have higher implantation rates in frozen embryo transfers, rather than fresh embryo transfers.”
Melbourne IVF fertility specialist Dr Genia Rozen told TMR that improving success rates were a positive sign for cancer survivors.
“It’s really encouraging, especially for a woman who is diagnosed with a serious medical condition like cancer, and who has not had the opportunity either to have a child or to complete her family,” she said.
“We can now have extra confidence based on the improvements that we’ve seen in this report that, if she goes through a cycle to freeze eggs or embryos, it’s more likely than ever that those eggs might one day help her have a pregnancy.”
Another key finding in the report was that multiple birth rates had decreased from 4.4% in 2015 to 2.9% in 2019, which Professor Chambers said was one of the lowest in the world.
This had largely been achieved through the shift to single embryo transfer. “Despite having relatively high utilisation rates of IVF, Australia is probably one of the safest countries in the world to have it,” she said.