A Benchtop Incubator Prospective Study

Overview

The use of extended embryo culture to the blastocyst stage and preimplantation genetic testing for aneuploidy (PGT-A) has enabled identification and selection of embryos with the best developmental potential and improved in vitro fertilization (IVF) clinical outcomes. While numerous types of commercially available human embryo culture media exist for culture to the blastocyst stage, the impact of culture conditions on blastocyst development and aneuploidy formation is not well understood. Culture conditions are very important for the success of the IVF cycle, many of the factors involved in the process have been extensively studied, including the use of sequential culture medium vs single step culture medium, humidified incubators vs dry incubators and refreshing the medium on day 3 vs uninterrupted culture till day 5. However, none of the studies investigated the effect on euploid rate in a sibling oocyte design with PGT-A, which requires culture till day 7.

It is considered a routine practice to grade the embryos on day 3 of development, which will require disturbing the culture conditions by annotating the embryos using inverted microscopes. Extended culture to day 7 is required in order to perform trophectoderm biopsy required for PGT-A. There are several culture factors that can affect embryo development, such as the pH, which is controlled through the concentration of CO2, and also the osmolality, which is the concentration of solute per liter of solution. Evaporation of the solution due to the exposure to high temperature (37°C) can change the concentrations and hence compromise embryo development. To reduce the rate of evaporation, culture droplets are covered with a layer of mineral oil. Humidified incubators can also reduce the rate of evaporation. However, in the case of dry incubators, such as benchtop incubators, replenishing the culture medium at least once -by moving the embryos to a new culture dish- during these 7 days of culture might be the solution. Since single-step medium is designed to sustain embryo development for 5 continuous culture days, while some laboratories culture embryos for 7 days, refreshing the culture medium is inevitable either on day 3 or day 5 of development. There is no concrete evidence on which of these practices will provide a better environment for embryo development. Moreover, none of the studies investigated the effect of single-step culture medium changeover on day 3 or day 5, on the chromosomal errors (aneuploidy/mosaicism). Investigators aim in this prospective sibling oocyte study, to explore which day of culture medium refreshment (day 3 or day 5) provides a higher rate of euploid blastocysts.