Waldenström 2009.

Methods	Prospective, randomised controlled trial
Participants	600 women undergoing IVF with at least 5 fertilised oocytes were randomised into a treatment group (n=197) and a control group (n=199) participants. 173 participants were excluded because they did not meet the inclusion criterion of  at least 5 fertilised oocytes and 31 participants withdrew from the trial. Unclear whether oocyte donations were included. The patients had previous treatments but no frozen oocytes were used for this trial.
Interventions	Blastocyst culture in atmospheres with either 6% CO2 in air (˜19% O2) or 6% CO2, 5% O2, 89% N2. Embryo transfer at Day 5.
Outcomes	Live birth rate, clinical pregnancy rate (reported as viable pregnancies), multiple pregnancies, miscarriages, fertilization rate, embryo development (high quality blastocysts) and cryopreservation rate.
Notes	Location: Sweden Setting: In Vitro Fertilization Unit, Falun Hospital Funding is unclear
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method of randomisation not described
Allocation concealment (selection bias)	Unclear risk	Not described
Blinding (performance bias and detection bias) All outcomes	Low risk	The clinician was blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	Follow up until delivery, loss to follow up accounted for, no intention‐to‐treat analysis
Selective reporting (reporting bias)	Unclear risk	Results are not described in a prespecified manner
Other bias	Low risk	Multiple pregnancy rate is reported with a multiple embryo transfer policy