Ng 2005.

Study characteristics
Methods	Randomised trial
Participants	160 women from Hong Kong with frozen embryo transfer Mean age: 34.0 years
Interventions	Laser‐assisted thinning 1/4 with frozen embryos compared to frozen embryos AH: 80 women Control: 80 women
Outcomes	Clinical pregnancy, miscarriage, multiple pregnancy rates
Notes	No study author contact as all details clearly stated in article No. of embryos stated: AH, transferred 2 in 52.5% and 3 in 41.3%; control, transferred 2 in 36.2% and 3 in 61.3%
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated randomisation
Allocation concealment (selection bias)	Unclear risk	'Sealed envelopes' used but unclear if these were opaque and how they were numbered
Blinding (performance bias and detection bias) All outcomes	Low risk	Double‐blinding until completion of the study
Incomplete outcome data (attrition bias) All outcomes	Low risk	No evidence of attrition bias
Selective reporting (reporting bias)	Unclear risk	Original protocol not viewed. Study authors did not report on live birth
Other bias	Low risk	None identified