Chances of successful pregnancy are the same with embryo transfer on day three or five

One out of thirty children in the Netherlands is conceived via in vitro fertilization, or IVF for short. In this procedure, egg cells are fertilized outside the body and grown in the laboratory for several days. One or more embryos are then transferred back in the uterus and the rest is frozen. Traditionally, the laboratory phase lasts three days. Due to technical improvements, embryo transfer is now also possible after five days. The idea is that only viable embryos remain after five days, which increases the chance of a successful pregnancy. However, this leaves fewer embryos in the freezer.

Previous research has shown that the chance of success after the first transfer is indeed higher when this takes place on day five than on day three. But these studies did not evaluate the results of the entire IVF trajectory, including any subsequent transfer of frozen embryos. Research by Radboud university medical center, carried out in collaboration with Amsterdam UMC, changes this.

The same number of pregnancies

The study was conducted in 21 Dutch IVF centers among more than 1,200 women. At least four embryos had to be available for transfer two days after fertilization. In half of the women, embryos were transferred on day three, in the other half on day five. The outcome was the chance of a successful pregnancy during the entire IVF trajectory. This turned out to be the same in both groups, around sixty percent.

Researcher Simone Cornelisse explains the results: 'Ultimately, IVF is about a successful pregnancy, and not only about the chances of success after the first transfer. Abroad, where IVF care is not insured, clinics often advertise their success rates from the first transfer on day five. In doing so, they provide an incomplete representation of the situation. Our study shows that women should have a choice about the moment of transfer.'

Personal decision

Other results from the study may influence that choice. As in previous research, there was a higher chance of a successful pregnancy after the first transfer on day five. There were also fewer miscarriages in that group. On the other hand, if the embryos were transferred on day three, more could be frozen for later use and the risk of premature birth was somewhat lower. Both choices have advantages and disadvantages, but do not make any difference to the overall success rate.

'It is a very personal decision', says clinical embryologist Liliana Ramos, one of the study leaders. 'For some people, getting pregnant as quickly as possible is very important, for example if the woman is older. Someone else attaches more value to a larger number of frozen embryos or wants to keep the chance of premature birth as small as possible. There is no guideline regarding the day of transfer. Therefore, a couple who want to become pregnant must discuss it with the doctor and make a choice together.'