While numerous types of commercially available human embryo culture media exist for human blastocyst culture, the impact of culture conditions on blastocyst development and aneuploidy formation is not fully understood. Culture conditions are very important for the success of the in vitro fertilization (IVF) cycle, many of the factors involved in the process have been extensively studied. However, none of the studies investigated the effect on euploid rate in a sibling oocyte design with preimplantation genetic testing for aneuploidy (PGT-A), which requires culture till day 7. In addition, the clinical outcome (implantation) will be investigated in a frozen cycle regimen. Hence, the study will explore which day of media refreshment will result in higher rate of ploidy and would improve clinical outcomes. Investigators aim at exploring the best practice, that would empower the euploid rate through the comparison of refreshing the single-step medium on day 3 or day 5 in a sibling oocyte prospective design.

The use of extended embryo culture to the blastocyst stage and PGT-A has enabled identification and selection of embryos with the best developmental potential and improved IVF clinical outcomes. 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. However, the application of Time-lapse technology (TLS) allows annotating the embryos on day 3 without interrupting the culture conditions, especially if TLS is combined with single-step culture medium.

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.

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). We aim in this study to explore which day of culture medium refreshment (day 3 or day 5) provides a higher rate of euploid blastocysts.

Summary about data collected. Categorical data will be presented in frequency tables and histograms. Continuous values will be summarized according the mean, standard deviation and confidence interval.

Inclusion Criteria:

• Patients with a minimum of 8 - 10 follicles during ovarian stimulation
• Patients with a minimum of 8 mature oocytes
• PGT-A
• ICSI
• BMI<35
• Age 18- 40
• Fresh or frozen ejaculatory sperm >10,000 motile sperm
• Any Ovarian stimulation
• Embryos cultured in Time-lapse system

Exclusion Criteria:

• PGT-M or PGT-SR
• Previous history of embryo arrest
• Endometriosis
• Hydrosalpinx
• History of uterine abnormality or previous uterine surgery
• History of previous treatment which may impact the ovarian reserve (adnexal surgery, chemotherapy, radiation…)

Patients undergoing a fertility treatment due to primary or secondary infertility at ART Fertility Clinics.