Traditionally, embryos are transferred to the uterus three days after fertilization during IVF treatment. Due to improvements in laboratory techniques, this is now also possible after five days. Half of the Dutch assumed that this increases the chance of a successful pregnancy. However, a study by the Radboud University Medical Center and the Amsterdam UMC shows that the day of transfer has no influence on the success rate of IVF treatment. One in every 30 children in the Netherlands is conceived through in vitro fertilization, or IVF for short.
How Embryo Transfer and Pregnancy Chances are Related
In this procedure, eggs are fertilized outside the body and cultured in the laboratory for several days. One or more embryos are then transferred back into the uterus and the rest are usually frozen. Traditionally, the laboratory phase lasts three days. Due to technical improvements, the embryo transfer can now also take place after five days. The idea is that after five days, only viable embryos will remain, increasing the chance of a successful pregnancy. However, fewer embryos will remain in the freezer.
Previous research has shown that the chances of success after the first transfer are actually higher when this takes place on day five than on day three. However, these studies did not evaluate the results of the entire IVF process, including a later transfer of frozen embryos. The research conducted by the Radboud University Medical Center, in collaboration with the Amsterdam UMC, changes this.
Same Number of Pregnancies
The study was conducted in 21 Dutch IVF centers with more than 1,200 women. At least four embryos had to be available for transfer two days after fertilization. In half of the women, the embryos were transferred on the third day, in the other half on the fifth day. The outcome was the chance of a successful pregnancy during the entire IVF process. This was about sixty percent in both groups.
Researcher Simone Cornelisse explains the results: “Ultimately, IVF is about a successful pregnancy and not just about the chances of success after the first transfer. Abroad, where IVF treatment is not covered by insurance, clinics often advertise their success rates from the first transfer on day five. In doing so, they present an incomplete picture of the situation. Our study shows that women should have a choice about when the transfer takes place.”
Pros and Cons
Other findings from the study may influence this decision. 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 this group. On the other hand, when embryos were transferred on day three, more could be frozen for later use and the risk of premature birth was slightly lower. Both decisions have advantages and disadvantages, but do not affect the overall success rate.
According to clinical embryologist Liliana Ramos, one of the study leaders, it is a very personal decision. For some people, it is very important to get pregnant as quickly as possible, for example if the woman is older. Others place more value on having a larger number of frozen embryos or want to minimize the risk of premature birth. There is no guideline regarding the day of transfer. Therefore, a couple who want to get pregnant must discuss this with their doctor and make a decision together.
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