Although there is no universally accepted definition, RIF has often been described as two or three or more failed embryo transfers. A survey of clinicians and embryologists (Cimadomo et al. 2021) found that the most common definition is 3 failed fresh or frozen transfers.
The ESHRE good practice recommendations on RIF (2023) argue that this simple number-based approach is too rigid, since repeated implantation failure can be due to chance, patient factors, or clinic practices. Instead, they suggest looking at the cumulative chance of implantation. RIF is suspected once a patient has undergone enough embryo transfers that their predicted chance of implantation would normally be over 60%, but pregnancy has still not occurred. At this point, failure is less likely to be due to chance alone and further investigations may be warranted.
According to ESHRE’s recommendations, RIF can be considered under the following conditions:
- After 3 failed transfers in women under 35
- After 4 failed transfers in women aged 35–39
- After 6 failed transfers in women 40 and older
- If embryos have been tested with PGT-A and are euploid, RIF is suspected after two failed transfers regardless of age