Recurrent implantation failure: gamete and embryo factors.

Chromosomal abnormalities, sperm DNA damage, zona hardening, inadequate culture conditions, and suboptimal embryo development all play a significant role in the etiology of recurrent implantation failure. Evidence suggests that preimplantation genetic screening does not increase implantation or live birth rates. Comparative genomic hybridization array and analysis of single nucleotide polymorphisms could enable a more comprehensive screening of chromosomes. Assisted hatching may help to overcome zona hardening in selected cases. Optimal culture conditions and blastocyst transfer could contribute toward improving implantation and pregnancy rates. Novel embryo assessment and selection procedures, such as time-lapse imaging and metabolomics, may help in better evaluation of embryo quality and viability and help in selecting embryos with the highest implantation potential. The safety and efficacy of emerging treatment modalities should be evaluated in prospective randomized clinical trials before being applied in routine clinical practice.