Fresh Embryo Transfer Yields Higher Live Birth Rates Than Freeze-All Strategy in Women with Low IVF Prognosis: Study
China: A randomized clinical trial conducted at fertility centers in China assessed live birth rates following fresh versus frozen embryo transfers in women with a low probability of in vitro fertilization (IVF) success. Published in The BMJ, the study found that 40% of women who underwent fresh embryo transfer had a viable live birth, compared to 32% in the frozen embryo transfer group. The fresh transfer group demonstrated higher pregnancy rates and a greater cumulative live birth rate within one year of randomization.
The approach of freezing all viable embryos before transferring them to the uterus, known as the “freeze-all strategy,” has gained widespread use in in vitro fertilization over the past decade. However, it may not be the most suitable option for everyone. Considering this, Daimin Wei, Key Laboratory of Reproductive Endocrinology, Ministry of Education, Shandong University, Jinan, China, and colleagues aimed to evaluate whether a freeze-all strategy enhances the likelihood of live birth compared to fresh embryo transfer in women with a low prognosis for IVF treatment.
For this purpose, the researchers conducted a multicentre, randomised controlled trial across nine fertility centers in China, involving 838 women with a low IVF prognosis. Participants, defined by poor ovarian reserve or retrieval of ≤9 oocytes, were randomly assigned to either a frozen or fresh embryo transfer group. The frozen group underwent embryo cryopreservation for later transfer, while the fresh group received embryo transfer immediately after oocyte retrieval.
The primary outcome was live birth at ≥28 weeks gestation. The secondary outcomes included clinical pregnancy rates, pregnancy loss, ectopic pregnancy, birth weight, maternal and neonatal complications, and cumulative live birth rates within one year of randomisation.
The key findings of the study were as follows:
- The live birth rate was lower in the frozen embryo transfer group (32%, 132 of 419) than in the fresh embryo transfer group (40%, 168 of 419) (relative ratio: 0.79).
- The clinical pregnancy rate was lower in the frozen embryo transfer group (39%, 164 of 419) compared to the fresh embryo transfer group (47%, 197 of 419) (relative ratio: 0.83).
- The cumulative live birth rate was lower in the frozen embryo transfer group (44%, 185 of 419) than in the fresh embryo transfer group (51%, 215 of 419) (relative ratio: 0.86).
- No significant differences were observed in birth weight, obstetric complications, or neonatal morbidities between the two groups.
The researchers found that fresh embryo transfer may be a more suitable option for women with a low prognosis for IVF, as it resulted in a higher live birth rate compared to the freeze-all strategy. Unlike previous findings in women with a good prognosis, this study demonstrated that a freeze-all approach led to lower live birth rates in this specific patient group.
"The results do not support the routine use of the freeze-all strategy in women with a low prognosis. To determine their impact on reproductive outcomes, further research is needed to evaluate treatment strategies that delay fresh embryo transfer, such as accumulating embryos through back-to-back cycles or performing routine preimplantation genetic testing for aneuploidy," the researchers concluded.
Reference:
Wei D, Sun Y, Zhao H, Yan J, Zhou H, Gong F, Zhang A, Wang Z, Jin L, Bao H, Zhao S, Xiao Z, Qin Y, Geng L, Cui L, Sheng Y, Sun M, Liu P, Ding L, Liu H, Wu K, Li Y, Lu Y, Xu B, Xu B, Zhang L, Zhang H, Legro RS, Chen ZJ. Frozen versus fresh embryo transfer in women with low prognosis for in vitro fertilisation treatment: pragmatic, multicentre, randomised controlled trial. BMJ. 2025 Jan 29;388:e081474. doi: 10.1136/bmj-2024-081474. PMID: 39880462; PMCID: PMC11778674.
