A review of factors influencing the implantation of euploid blastocysts after in vitro fertilization

This is a comprehensive review of the current literature addressing factors that are involved in the successful implantation of euploid blastocysts. It includes a comprehensive analysis of published studies on laboratory factors that may impact the performance of euploid blastocysts, including morphology, day of biopsy, and rebiopsy. Preexisting underlying patient factors that may impact the outcome of the embryo transfer (ET) of euploid blastocysts are also explored, including body mass index and endocrine abnormalities. The role of the uterine environment and its potential impact on the successful implantation of euploid blastocysts are reviewed, including endometrial thickness and pattern, uterine architecture, and adenomyosis. Finally, published studies on the stimulation environment and methods of endometrial preparation for frozen ET are analyzed. Euploid embryos appear to have similar outcomes regardless of maternal age (up to the age of approximately 40 years), frozen-thawed ET protocol (in ovulatory women), stimulation or trigger type, or culture conditions. Decreased implantation rates may be expected from euploid blastocysts with poorer morphology, those biopsied on day 7, those twice biopsied/frozen, and those after a difficult ET. Patients with very advanced age, high body mass index, adenomyosis, polycystic ovary syndrome, and possibly methylenetetrahydrofolate reductase carriers may be at higher risk of euploid implantation failure or early pregnancy loss. This analysis only applies to those who are able to produce euploid blastocysts. There is a lack of evidence to support any interventions that subsequently increase implantation.