Silverberg 2005.

Methods	Prospective, randomised controlled trial
Participants	Patients undergoing IVF (n=126). Inclusion and exclusion criteria were not stated. Information on previous treatments is not provided.
Interventions	Embryos were grown in either 6% CO2, 5% O2 and 89% N2 or in 5% CO2 in air. Embryo transfer at Day 2/3.
Outcomes	Embryo development, cryopreservation rate and ongoing/delivered pregnancy rate.
Notes	Location: USA Setting: Texas Fertility Center Group sizes not reported Study published as conference abstract No commercial funding
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method of randomisation has not been described
Allocation concealment (selection bias)	Unclear risk	Not described
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Not described
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Length of follow up unclear, loss to follow up unclear and ITT analysis unclear
Selective reporting (reporting bias)	Unclear risk	Not described
Other bias	High risk	Multiple pregnancy rate is not reported, while multiple embryos are transferred