Exploring Single Step Culture Medium Refreshment Effect on Embryo Ploidy Rate: A Benchtop Incubator Prospective Study

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.