Cohen 1992.

Study characteristics
Methods	Single centre Unclear whether power calculation performed ITT analysis unclear Published as full paper
Participants	330 women from North America undergoing IVF Mean age: control group 36.7 (3.7); AH group 36.5 (3.3)
Interventions	AH by acid Tyrode's (chemical; complete zona breach hole; 68 to 72 hour egg retrieval to AH; 4 to 8 hours AH to transfer), 69 women with FSH < 15 (trial 1), 80 women with poor prognosis (trial 2, thick zona pellucida, low developmental rate, excessive fragmentation), 15 women with FSH > 15 (trial 3) No AH, 68 women with FSH < 15 (trial 1), 83 women with poor prognosis (trial 2, thick zona pellucida, low developmental rate, excessive fragmentation), 15 women with FSH > 15 (trial 3)
Outcomes	Implantation, clinical pregnancy (rates given for trials 1, 2, and 3), live births (rates given for women in trial 1 only), multiple pregnancy (rates given for women in trials 1 and 2 only)
Notes	Attempted to contact author about this study. Reply received, but no additional information offered No. of embryos: AH 3.5; control 3.4
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Pre‐printed randomisation list
Allocation concealment (selection bias)	Unclear risk	Unclear
Blinding (performance bias and detection bias) All outcomes	Low risk	Participants blinded Assessor blinded
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No evidence of post‐randomisation exclusions, but timing of allocation unclear
Selective reporting (reporting bias)	Low risk	Original protocol not viewed. Live birth reported
Other bias	Low risk	None identified