Sequential Blastocyst Transfer: Live-Birth Benefit Remains Unclear

For patients who have experienced repeated IVF implantation failure, transferring two blastocysts one day apart was associated with a higher clinical pregnancy rate than transferring both on the same day. However, the overall live-birth rate did not differ significantly.

The retrospective study included 639 frozen embryo-transfer cycles. The sequential approach involved transferring one blastocyst on the fifth day after progesterone began and the other on the sixth day, potentially exposing embryos to the endometrium at two different points in its implantation window.

Among women with exactly three previous failed transfers, live birth was 41.7% with conventional transfer and 58.4% with sequential transfer. That subgroup finding needs caution: this was a single-center observational study, not a randomized trial, and it does not establish a new standard treatment.

Why transfer two embryos a day apart?

Researchers at Hebei Maternity Hospital in China analyzed patients with recurrent implantation failure who underwent frozen embryo transfer between May 2018 and December 2023.

In the conventional group, two blastocysts were transferred on the same day. In the sequential group, one blastocyst was transferred on day five of progesterone exposure and the second on day six.

The investigators used propensity-score matching to make the groups as comparable as possible. Matching considered age, body mass index, duration of infertility, anti-Müllerian hormone (AMH), the number of previous failed transfers, endometrial thickness and blastocyst quality. The final comparison included 272 conventional-transfer and 272 sequential-transfer cycles.

Clinical pregnancy increased from 54.4% to 65.4%

The clearest difference was in clinical pregnancy. The rate was 54.4% when both blastocysts were transferred together and 65.4% when they were transferred one day apart: an approximately 11-percentage-point difference that was statistically significant.

The proportion of clinical pregnancies that were multiple pregnancies was lower with sequential transfer: 30.9%, compared with 45.9% in the conventional group.

However, there was no clear difference in live birth, one of the most important treatment outcomes. Overall live-birth rates were 44.1% with conventional transfer and 50.4% with sequential transfer. The 6.3-percentage-point numerical difference was not statistically significant.

Implantation rates were likewise not significantly different: 39.5% and 43.0%, respectively.

The findings therefore should not be interpreted as proof that transferring embryos a day apart increases the chance of having a baby.

An exploratory live-birth difference after exactly three failures

A different pattern appeared when patients were divided according to their previous failed transfers.

Among women with exactly three previous failures, live birth was 41.7% in the conventional group and 58.4% in the sequential group.

For patients with more than three previous failures, clinical pregnancy was 40.9% with conventional transfer and 63.3% with sequential transfer.

Among women aged 40 or older, clinical pregnancy was 31.7% versus 57.7%, respectively.

These subgroup analyses involved smaller numbers and must be interpreted cautiously. The investigators described them as exploratory because statistical power was limited and multiple comparisons were made. Larger studies are needed to establish whether the apparent benefits are reproducible.

Two opportunities to meet the implantation window

Why might moving the timing of the same two embryos make a difference?

The proposed explanation involves the window of implantation: the interval when the endometrium is most receptive to an embryo.

This interval may not occur at exactly the same time in every woman. In some patients with repeated implantation failure, it has been proposed that endometrial readiness occurs earlier or later than generally expected.

When both blastocysts are transferred together, they encounter a similar endometrial timing. Transferring them a day apart exposes them to different points in that interval. Rather than relying on one moment, the strategy effectively makes two attempts to meet the implantation window on consecutive days.

The first transfer might also cause small endometrial changes that influence the environment encountered by the second embryo. These explanations remain hypotheses. The study did not establish the mechanism by which sequential transfer might work.

Sequential transfer is not yet an established standard for RIF

The limitations are substantial. This was a retrospective analysis of treatment records from one Chinese hospital, not a randomized controlled trial. Propensity-score matching reduced measured differences between the groups, but unmeasured factors may still have affected the outcomes.

Transferring embryos on consecutive days also means undergoing two procedures. Further research is needed on cost, inconvenience and the safety of passing a catheter through the cervix twice.

Most importantly, clinical pregnancy was significantly higher, but overall live birth was not.

The appropriate interpretation is that changing transfer timing may influence pregnancy outcomes for some patients with previous implantation failure. The results do not show that sequential transfer is necessarily the better treatment for such patients.

Large prospective randomized trials will need to establish whether the approach improves live birth as well as clinical pregnancy, and assess its safety, before its clinical value becomes clearer.

This article is based on the Hebei Maternity Hospital study published in Frontiers in Endocrinology on September 24, 2026. Because it was a single-center retrospective study, its findings cannot definitively establish the effectiveness or safety of sequential blastocyst transfer.

Research references

Sequential blastocyst transfer improved pregnancy outcomes in patients undergoing frozen-thawed embryo transfer cycles: who will be the ultimate beneficiary. Frontiers in Endocrinology 17:1782118, September 24, 2026. DOI: 10.3389/fendo.2026.1782118.