Chances of pregnancy success are the same with embryo transfer on day 3 or day 5, study finds

In IVF treatment, embryos are traditionally transferred into the uterus three days after fertilization. Thanks to advances in laboratory technology, this is now also possible after five days. This is believed to increase the chances of a successful pregnancy.

A study conducted by Radboud University Medical Center and UMC Amsterdam shows that the day of transfer does not influence the success rate of the IVF course. The results were published in BMJ

In the Netherlands, one in 30 children is conceived through in vitro fertilization, or IVF for short. In this procedure, eggs are fertilized outside the body and grown in a laboratory for several days. One or more embryos are then reintroduced into the uterus and the rest are frozen.

Traditionally, the laboratory phase lasts three days. Thanks to technical advances, embryo transfer is now also possible after five days. The idea is that only viable embryos remain after five days, which increases the chances of a successful pregnancy. However, this leaves fewer embryos in the freezer.

Previous research has shown that the chances of success after the first transfer are indeed higher when it takes place on day five than on day three. But these studies did not assess the results of the entire IVF journey, including the subsequent transfer of frozen embryos. Research from Radboud University Medical Center, in collaboration with UMC Amsterdam, is changing that.

The same number of pregnancies

The study was conducted in 21 Dutch IVF centres with more than 1,200 women. At least four embryos had to be available for transfer two days after fertilisation. In half of the women, the embryos were transferred on day three, in the other half on day five. The result was the chance of achieving a pregnancy throughout the IVF course. This result was the same in both groups, about sixty percent.

Researcher Simone Cornelisse explains: “Ultimately, IVF is about pregnancy success, not just the chances of success after the first transfer. Abroad, where IVF care is not insured, clinics often announce their success rates from the first transfer on day five. In doing so, they give an incomplete picture of the situation. Our study shows that women should have the choice of when to transfer.”

Personal decision

Other results from the study may influence this choice. As in previous research, the chances of successful pregnancy were higher after the first transfer on day five. There were also fewer miscarriages in this group.

On the other hand, if the embryos were transferred on the third day, it would be possible to freeze them further for later use and the risk of premature birth would be slightly lower. Both options have advantages and disadvantages, but they do not affect the overall success rate.

“It’s a very personal decision,” says clinical embryologist Liliana Ramos, one of the study’s leaders.

“For some people, it is very important to get pregnant as soon as possible, for example if the woman is older. Others attach more importance to a larger number of frozen embryos or want to minimise the risk of premature birth. There are no guidelines regarding the day of transfer. Therefore, a couple who want to get pregnant should discuss this with their doctor and make a choice together.”