Previous studies in human and different mammals have proved that the embryo group culture (in the same culture medium drop) using a reduced volume is associated with a better embryo development. This is due to the effect of different autocrine and paracrine factors secreted by the embryos. Besides, previous studies with embryos from human and other mammals have shown that a high oxygen concentration may have a negative effect on embryo quality due to the generation of reactive oxygen species, which cause oxidative stress. The embryo culture at low oxygen tension is correlated to better success rates in IVF/ICSI treatments.

The purpose of this study is to evaluate the combined effect of the embryo group culture and the low oxygen tension on the embryo development and the results of the IVF/ICSI treatments. The specific goal is to compare the embryo group culture in a reduced volume of medium at a low oxygen tension (5%) with the standard individual culture at an atmospheric oxygen tension (20%). The first culture condition will be applied in a K-MINC incubator (COOK Medical®), whereas the second condition will be applied using a Heracell incubator (Heraeus®).

Inclusion Criteria:

• <38 years (with own oocytes) / <45 years (with oocyte donation).
• First treatment with own oocytes / any treatment with oocyte donation.
• ≥10 oocytes with a diameter of ≥10 mm.

Exclusion Criteria:

• Diseases that affect endometrial receptivity: endometriosis, hydrosalpinx, ovarian hyperstimulation syndrome, obesity, endocrinopathies, thrombophilia, congenital or acquired uterine anomalies.
• Patients under a treatment with genetic preimplantation diagnosis.