Adding a low-quality blastocyst to a high-quality blastocyst for a double embryo transfer does not decrease pregnancy and live birth rate

Introduction: The effect of embryo quality on clinical outcomes of assisted reproductive technology following a double transfer is not well defined, with some studies suggesting that a low-quality embryo transferred with a high-quality embryo decreases the live birth rate (LBR), compared with transferring a single high-quality embryo. Our study examined whether the quality of a second blastocyst transferred affects the outcome, controlling for the number of the available high-quality blastocysts (HQB).

Material and methods: A historical cohort study of 2346 fresh blastocyst transfers in a single fertility clinic between 2013 and 2019. The main outcomes were pregnancy, miscarriage, live birth, and multiple gestation rates. Outcomes were compared between single embryo transfers with a high-quality blastocyst (SET-H), double embryo transfers with two HQBs (DET-HH), and transfers with one high-quality and one low-quality blastocyst (DET-HL). Outcomes were also assessed between SET and DET when only low-quality blastocysts were available.

Results: With one HQB available, DET-HL increased LBR (adjusted odds ratio [OR] 1.65, 95% CI 1.09-2.49) compared with SET-H, but increased multiple gestation rate (aOR 23.1, 95% CI 3.0-177.6). With two HQBs available, DET-HH was associated with a higher LBR (aOR 1.62, 95% CI 1.28-2.04) and lower miscarriage rate (aOR 0.56, 95% CI 0.40-0.80), but very high twin rate (aOR 49.8, 95% CI 24.3-102.1) compared with SET-H. A SET-H with at least one or more HQB available to freeze, compared with a SET-H with no other HQB available, had a higher LBR (aOR 1.69, 95% CI 1.17-2.45). When there were no HQBs available, compared with SET-L, a DET-LL had a higher live birth (aOR 3.20, 95% CI 1.78-7.703) and twin rate (aOR 3.72 × 10¹⁰ ) and a lower miscarriage rate (aOR 0.24, 95% CI 0.10-0.58).

Conclusions: When there is one HQB available, transferring an additional low-quality blastocyst would only slightly increase the LBR, but significantly increase the twin rate, therefore SET should be recommended. When two or more HQBs are available, SET-H would have a reasonably good chance of success without the very high twin rate associated with DET-HH. DET-LL when compared with SET-L, would increase the LBR, but increase the risk of multiple gestation.