Myriads of elements affect human embryo culture in vitro. These include, but not limited to, air quality, culture media, culture temperature, incubator humidity, pH, and O2 levels. O2 tension has been thoroughly investigated and, to date, 5% O2 level is superior to 20%. Reports showed that lowering the O2 from Day 3 of embryo culture seems to be physiological.

Inclusion Criteria:

• ICSI cycles undergoing their first ICSI attempt

Exclusion Criteria:

• ICSI cycles with a previous failure