Cumulative live birth rates after up to 15 transfers with untested embryos

A 2025 study compared cumulative live birth rates for patients transferring up to 15 untested embryos. Besides the CLBR based on single blastocyst transfers and age, they found differences based on ovarian response and blastocyst formation rates. They also suggested a new way to define recurrent implantation failure.

Cumulative live birth rates (CLBR) refer to the overall chance of a live birth after a number of transfers. It often refers to the overall chance after transferring all available embryos.

This post is a summary of a study by Dhaenens et al. (2025), who measured CLBR after up to 15 consecutive transfers of untested embryos. This research also provides insights into the incidence of recurrent implantation failure, because if the data plateaus, this would show that some patients are unable to have a live birth despite repeated transfers.

Note that most of the data in this post was visually estimated from graphs (I can’t post the graphs due to copyright), so there could be small errors that deviate from the original data.

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Study details

This section covers key details of how the study was performed, including patient characteristics, how they were treated, and other methods used. For those who aren’t interested in these details, and just want to see the results, you can go ahead and skip this part.

• This is a retrospective cohort study that took place at a single Belgium IVF center, using data between 2010 and 2022.
• Inclusions: This study only included patients with at least two embryos transferred in at least two transfers.
• Exclusions: No PGT cycles, no egg donation, no surrogacy, no mixing of cleavage stage and blastocyst stage transfers.

In terms of sample size, there were 11,463 women who had 19,378 egg retrievals and 31,478 transfers. Based on age:

• 36 or younger: 7735 women (67.5%)
• 37-40: 2419 (21.1%)
• >40: 1309 (11.4%)

The data in this paper is based on a statistical model using Inverse Probability Weighting, which adjusts for potential biases like differences in patient characteristics that might affect the results, providing a more accurate representation of the cumulative live birth rates.

Cumulative live birth rates for cleavage or blastocyst stage, by age

For cleavage stage vs blastocyst stage transfers, they grouped patients into two age groups (≤36 and >36), and you can see the results below. Note that this included the total number of embryos transferred, including transfers with multiple embryos (in other words, if one transfer involved 2 embryos and another included 1 embryo, then this would be 3 in total).

Let’s walk through this a bit so it’s clear for this data and other related data in this post. This is showing the cumulative live birth rate, or the overall live birth rate, after an increasing number of embryo transfers. For the “Age ≤36, blastocyst stage” group, after 1 embryo was transferred, the live birth rate was 32% for the group. After a total of 3 embryos were transferred, the overall (cumulative) live birth rate increased to 57% for the group. After 5 were transferred, it was 70%, and so on!

This shows that the CLBR didn’t plateau! In other words, each transfer attempt increased the CLBR. There were smaller gains as the number of embryos transferred increased, but it kept going. Eventually, with more transfers it could potentially flatten out, but it didn’t with 15 transferred embryos. As we’ll see below, this changes when we consider age.

They performed a logistic regression analysis to identify any factors that could predict CLBR:

• Female age. Each increasing year, after age 33, decreased the odds of achieving implantation.
• Stage of embryo transfer. Transferring blastocysts over cleavage stage embryos increased the odds of achieving implantation.
• Embryo quality. Transferring excellent or good quality blastocysts increased the odds of implantation.
• No change with diagnosis.

More data! Cumulative live birth rates for single blastocyst transfers, by age

This study provided more data on age groups for single blastocyst transfers only, shown below. Note that some of this data ends at a certain transfer #, due to the small sample size — at some point, there just aren’t a lot of women doing transfers anymore, so the CLBR doesn’t increase.

This shows that there may be a plateau for CLBR based on age, particularly for women 38 and above (ie. around transfer 8 for 38-40, transfer 6 for 41-42 and transfer 4 for >42). However, the authors didn’t discuss this in any detail. The plateau suggests that having more transfers may not provide any additional increase to CLBR, although it isn’t clear if a lower sample size is influencing this trend.

Cumulative live birth rates change based on ovarian response, blastocyst formation rates

The researchers compared CLBRs among women with different ovarian responses to stimulation when transferring blastocysts.

• Ovarian response was defined as the number of eggs obtained from a retrieval: Excessive (>15 eggs), normal (10-15 eggs), suboptimal (4-9 eggs) and poor (<4 eggs).
• Women with normal or excessive responses reached a 50% CLBR after just two blastocyst transfers, while those with suboptimal or poor responses needed four transfers to achieve the same rate.
• More data if curious: At transfer #8, excessive and normal responders had about 80% CLBR, suboptimal had about 75% CLBR and poor responders had about 65% CLBR. At transfer #13, excessive and normal responders had about 85% CLBR, and suboptimal about 82% (poor responders dropped out at transfer 8, likely due to small sample size).
• After statistical adjustment for female age, the number, and the quality of previously transferred embryos, the chance of achieving a live birth from cycles with a poor response was 32% lower compared to cycles with a normal response.
• They also showed that younger women were more likely to make more eggs (ie. excessive/normal responders) and older women were more likely to produce fewer eggs (ie. suboptimal/poor responders).
• Question — They showed (1) that the suboptimal/poor responders had a lower CLBR, and (2) the suboptimal/poor responders were generally older, so is the lower CLBR because they’re older and their blastocysts are less likely to be euploid? Not quite! The researchers showed that patients younger than 36 also had differences in CLBR, even when they had a low/higher ovarian response. This suggests that low responders may inherently have lower egg quality than higher responders.
• Overall, the researchers found that women who are low responders need to have more blastocyst transfers to have the same CLBR as high responders. This was unrelated to age, so this result may be due to lower egg quality in lower responders.

The study also compared CLBR based on blastocyst formation rate:

• This was grouped into low (<33%), intermediate (33-66%), and high (>66%) categories, which I believe is % of eggs to blastocysts, although it wasn’t clearly stated.
• Patients with high or intermediate rates typically reached a 50% CLBR after three transfers, while those with low rates needed four.
• After adjusting for female age, number, and quality of embryos, the chance of a live birth from cycles with a low blastocyst formation rate was 32% lower compared to those with an intermediate rate, and was 28% higher in cycles with a high formation rate.
• This suggests that patients with higher % of blastocysts (from eggs) generally have blastocysts with a higher chance of implanting. For example, if Patient A and B both produce 10 eggs, but A makes 6 blastocysts and B makes 2, the blastocysts from A have a higher implantation potential.

Another analysis showed that the effectiveness of blastocyst transfers in achieving a live birth does not depend on the number of cycles it takes to gather those blastocysts. In other words, whether it takes one cycle or five cycles to collect enough eggs to transfer five blastocysts, the probability of achieving a live birth is similar.

Conclusions

This study compared CLBR for patients transferring blastocyst or cleavage stage embryos, finding the highest live births in younger patients transferring blastocysts.

They also looked at single blastocyst transfers, for a range of age groups, finding that patients <38 had around an 80% CLBR with 10 untested embryos transferred. The CLBR seemed to plateau for older women, possibly because of the smaller sample size.

The researchers suggest that RIF isn’t a black-and-white condition, and should be considered a risk factor that can affect each patient differently. They propose that RIF should be based on a threshold CLBR of 60% (or a cumulative pregnancy rate of 70%). In other words, RIF shouldn’t be defined by the same number of failed transfers for all patients, but instead should be defined by a personalized number of transfers that would result in a predicted CLBR of 60%. If you go back to the graph from earlier, this would be around 3 single blastocyst transfers for women <35, 4 transfers for women 35-37, and 7 transfers for women 38-40. The rationale here is that it takes this many untested single blastocyst transfers to achieve 60% CLBR, so if patients haven’t achieved it at that number of transfers, then there may be something else going on that isn’t just due to chance, and further treatment may be needed.

So what about women older than 40? This study didn’t really get into this, although it seems like there may be plateaus for older patients. Another study reviewed in my post in my post Cumulative live birth rates in women aged 40+, after up to 10 transfers addressed this for patients aged 40-45. They found that patients aged 41-45 plateaued at a certain point where the CLBR didn’t increase (around 8 for 41 and 42, and around 3 for 43-45). Another study, reviewed in my post Cumulative live birth rates in women aged 43+, after up to 10 cycles, found that the max cumulative live birth rate occurred around cycle 5 for women 43 and 44, then around cycle 2 for 45 and 46. Another post worth checking out is Study compares IVF cumulative live birth rates based on age, eggs retrieved, diagnosis. Apparently CLBR is a hot topic here on Remembryo! 🙂

A really interesting result in this study, I think, was the finding that CLBR was lower in patients with a low response vs a higher response. This was independent of age, and suggests that low responders may inherently have lower egg quality. The authors note that high responders may benefit from the recruitment of a larger and more diverse pool of follicles, and more supportive hormonal and follicular environment.

They also showed that women who had a higher blastocyst formation rate had a higher CLBR. Beebeejaun et al. (2023) found that women who had a higher number of excess blastocysts frozen after their first IVF cycle had a higher live birth rate, even after controlling for the number of eggs retrieved. This suggests that patients who are able to make more blastocysts may inherently have higher egg quality. To read more about this study, check my post Higher number of excess blastocysts frozen after IVF linked to higher live birth rates.

There’s a couple of related studies worth mentioning:

• Gill et al. (2024) found that women transferring up to 5 euploids consecutively had a CLBR of 98.1% (reviewed in my post “True” recurrent implantation failure is rare after five consecutive euploid embryo transfers). Applying the suggested 60% CLBR threshold for euploid transfers would mean that RIF could be considered after only a single euploid transfer! That’s because a single euploid transfer has a CLBR of 64.8%.
• Ata et al. (2021) used a mathematical model to predict CLBR when transferring untested embryos. They found that 6-9 blastocysts were needed to achieve a 95% CLBR for women <35 (reviewed in my post How many failed embryo transfers is too many?). The study in this post found that 9 transfers for women <35 resulted in a CLBR of 83%, which isn’t that far off from Ata et al.’s model.

Reference

L Dhaenens, R Colman, I De Croo, H Verstraelen, P De Sutter, D Stoop, Cumulative live birth rates of 31 478 untested embryos from 11 463 women challenge traditional recurrent implantation failure definitions, Human Reproduction, 2025;, deaf036, https://doi.org/10.1093/humrep/deaf036

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About Embryoman

Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.

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