In cattle less than 10% of the embryos develop to the blastocyst stage when embryos are cultured individually, however when bovine embryos are cultured in groups a typical 25-35% of blastocysts can be observed. This tendency, i.e. improved embryo development in group culture, has also been demonstrated in other mammalian species, such as mouse, cat and human. The main reason for this beneficial outcome of group culture has been ascribed to the presence of autocrine factors, which are factors secreted by preimplantation embryos that act upon the embryo itself or the neighboring embryos .

Although group culture systems are common in in vitro production systems for animal embryos, it is rarely done in human settings, where individual follow-up of the embryo during the whole culture period is of utmost importance. Recently a CE-labelled culture device has been designed for human embryos, that allow to combine the benefits of both group culture approaches and individual culture. The WOW dish is commercially available by Primo Vision and consists of 9 small microwells on the bottom of the plate, so that the embryos can be cultivated individually in a microwell, but covered by the same drop of culture medium.

In this clinical randomized trial, 158 patients will be included of which half of the fertilized oocytes will be cultured individually (standard culture system) and half of the fertilized oocytes will be cultured in group in a WOW dish, both during five days of culture. The aim of this study is to increase the number of blastocysts suitable for transfer or cryopreservation by culturing the embryos in WOW dishes.

Inclusion Criteria:

• Sperm obtained by ejaculation
• Conventional IVF/ICSI
• At least 10 fertilized oocytes (2 PN)

Exclusion Criteria:

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