Advanced Maternal Age and the Implantation Barrier
Maternal age remains the most potent predictor of IVF success. In women over 40, clinical pregnancy rates drop to approximately 19.39%, and miscarriage rates climb to over 36%, even when fertilization and embryo quality appear comparable to younger cohorts. This suggests that while embryo morphology may look 'good,' intrinsic chromosomal or energetic deficiencies often lead to failure.
Preimplantation genetic screening (PGS/PGT-A) has been employed to bridge this gap by selecting chromosomally normal embryos. However, evidence indicates that while PGT-A selects against aneuploidy, its impact on ultimate live birth rates in the RIF population is surprisingly negligible, suggesting that endometrial factors or embryo-endometrial cross-talk may be the remaining bottlenecks.
The RIF Threshold and Immune Interventions
The definition of Recurrent Implantation Failure (RIF) has historically been arbitrary. The 2023 ESHRE guidelines introduce a more rigorous 60% cumulative predicted failure threshold before invasive investigations are triggered. This shift aims to prevent premature medicalization of couples who may simply be on the wrong side of statistical probability.
For those meeting the criteria, immune-modulating interventions like PBMC infusion and G-CSF administration have shown promise. Interestingly, high-level evidence now discourages the use of assisted hatching or LMWH for RIF patients, focusing instead on the intrauterine environment and immune receptivity markers such as CD56+ uNK cells, though their predictive value for individual outcomes remains debated.
Hyaluronan-Enriched Transfer Medium: Panacea or Placebo?
Hyaluronan-enriched transfer medium (HETM), often marketed as 'EmbryoGlue,' is one of the most contested adjuncts in the field. High-quality RCTs and sensitivity analyses accounting for study bias have recently failed to show a statistically significant benefit for the general population (RR 1.06-1.14).
However, the evidence landscape for HETM is highly stratified. Subgroup analyses suggest potential benefits for patients with RIF, AMA, or intramural fibroids exceeding 4 cm. These findings highlight the need for targeted application rather than routine use. Furthermore, the mechanics of the transfer itself remain paramount: bed rest is now confirmed as detrimental, while ultrasound guidance is non-negotiable for optimizing success.
- Bed rest significantly reduces success (RR 0.857).
- HETM shows potential only in targeted subgroups (AMA/RIF/Fibroids).
- Retransfer of retained embryos carries lower success and higher ectopic risk.