Transferring frozen embryos a day earlier during IVF can dramatically boost success rates, research suggests.
A study led by Professor Tim Child, medical director at Oxford Fertility, found that transferring embryos on day six instead of day seven could double the IVF success rate.
The research specifically involved natural frozen embryo transfer – which studies suggest is just as successful as transfers involving medication.
This natural method involves relying on a woman’s own menstrual cycle, thereby avoiding the need for medicines and any potential side-effects.
The new study, being presented at the Fertility 2020 conference in Edinburgh and shared with the PA news agency, involved data from 561 frozen embryo transfers.
It found that those women who underwent embryo transfer six days after a surge in their body’s luteinizing hormone (which triggers ovulation) were far more likely to have a successful pregnancy beyond 24 weeks gestation than those whose transfer occurred on day seven.
Some 45% of women in the first group went on to have an ongoing pregnancy beyond 24 weeks, compared with 29.1% of women in the seven-day transfer group.
Once the woman’s age and other factors were taken into account, the ongoing pregnancy success rate was twice as high in the first group compared to the second.
Prof Child said: “This research not only reveals the best time for implantation in a natural cycle, when the body is most ready to receive an embryo, but also demonstrates how we can achieve very good pregnancy rates with a natural, drug-free treatment.”
He said a natural cycle involves working out the best time to thaw out a frozen embryo and relies on the woman’s natural menstrual cycle.
“This works for women who have regular menstrual cycles, which means it is suitable for most women,” he said.
“Our previous research has shown that that a medicated frozen cycle and a natural cycle have the same success rate.
“Most clinics are not doing a natural cycle, they are doing medicated or a natural cycle plus drugs.
“What we’ve shown is a true natural cycle with no drugs can really work with good success rates.
“You don’t need to be subjecting women to medications, hormones and pessaries.”
Prof Child said there was an “assumption” by some clinicians and patients that medications are needed for a frozen embryo transfer.
“We’ve shown that that’s not the case,” he said.
The women in the study were aged 36 on average.
Of the 561 cycles, 180 involved transfer on day six while 381 involved a transfer on day seven.
The miscarriage rate was similar between the two groups.
Dr Jane Stewart, chairwoman of the British Fertility Society, said: “This research seeks to answer an important question about the timing of embryo transfer when using frozen embryos.
“At present, it doesn’t justify a change in clinical practice.
“It does add an important element to the body of knowledge on this issue.”