Hurst 1998.

Study characteristics
Methods	Single‐centre randomised trial
Participants	20 women from North America undergoing IVF with no prior IVF (30 years or less, FSH < 10 IU/L, normal endometrium and sperm) or with prior IVF (35 years or less, 6 embryos, 50% fertilisation, normal endometrium). Mean age: control group 30 (0.8); AH group 30 (0.9)
Interventions	AH by acid Tyrode's (chemical; complete zona breach hole; ? hour egg retrieval to AH; ? hour AH to transfer) vs no AH AH: 13 women randomised, 52 embryos transferred Control: 7 women randomised, 28 embryos transferred
Outcomes	Implantation, clinical pregnancy, live births
Notes	Attempted to contact author about this study. A reply including much useful additional information was received No of embryos transferred: AH 4.0; control 4.0 Unclear whether power calculation performed ITT analysis unclear Published as full paper
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐randomised
Allocation concealment (selection bias)	Unclear risk	Unclear; no details
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Participants not blinded or unclear Assessor not blinded or unclear
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	ITT analysis unclear
Selective reporting (reporting bias)	Low risk	Protocol not viewed but outcomes reported including live birth
Other bias	Low risk	None identified