There is not yet a standardized system of human embryonic culture in vitro. In addition, technical improvements continually appear. The investigators recently carried out a study in which it shows that the grouped embryo culture at low oxygen tension (5% O2) in a benchtop incubator shows better success rates than individual culture at atmospheric oxygen tension (20% O2) in a conventional incubator. For these reasons, the investigators have decided to continue this research line to evaluate the efficacy of a new ART station with a closed environment in comparison of an open flow cabinet. This new system keeps a controled environment maintaining a carbon dioxide (CO2) concentration of 6% and a temperature of 37 degrees. A prospective randomized study will be carried out in which the manipulation of the gametes and pre-embryos of the patients will be carried out in open laminar flow cabinets or in a closed station that maintain the CO2 and temperature conditions.

Inclusion Criteria:

• Signing a written consent to participate in the study.
• Blastocyst transfer:
• Patients using their own oocytes under 40 years.
• Patients using donated oocytes.

Exclusion Criteria:

• Preimplantation genetic screening patients.
• Severe male factor (spermatozoa of testicular or epididymal origin, patients with cryptozoospermia and patients with retrograde ejaculation)