Cohen 1992.

Methods	Single centre Unclear if 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 tyrodes (chemical; complete zona breach hole; 68 to 72 hours 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 zonae 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 zonae 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 form women in trials 1 and 2 only)
Notes	Attempted to contact author about this study. Reply received, but no additional information was offered No. of embryos AH 3.5; Control 3.4
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Pre‐printed randomisation list day not stated
Allocation concealment (selection bias)	High risk	Allocation concealment inadequate
Blinding (performance bias and detection bias) All outcomes	Low risk	Participants blinded Assessor blinded
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	ITT analysis unclear
Selective reporting (reporting bias)	Unclear risk	Original protocol not viewed