| Study | Reason for exclusion |
|---|---|
| Abdelmassih 2002 | Pooled oocytes, then randomised; no per woman data provided |
| Amorocho 2012 | Compares technique of hatching with thickness of ZP on Day 3 of embryo development. Further details asked for but no response from study authors |
| Antinori 1996a | Not a randomised controlled trial Mentions randomly selected, not randomly allocated |
| Antinori 1996b | No randomised comparison between control and assisted hatching groups |
| Balaban 2002 | Not randomised No appropriate controls |
| Bider 1997 | Not randomised |
| Blake 2001 | Not randomised No embryo transfer occurred, so no review outcomes could be measured |
| Carter 2003a | No per woman data |
| Chao 1997 | Assessment of pregnancy was by hCG only 14 days after embryo transfer |
| Check 1996 | Not randomised Benefits of AH confounded by concurrent assessment of 2 different culture media |
| Chen 1999 | Not randomised Benefits of assisted hatching confounded by concurrent assessment of 2 different culture media |
| Chimote 2013 | Compared techniques of hatching. No information regarding randomisation method; does not suggest it is a randomised study |
| Cieslak 1999 | Comparison of 2 types of assisted hatching; no 'no assisted hatching' control group was used More than 1 cycle per woman |
| Cohen 1990 | Not randomised |
| Debrock 2011 | Primary outcome was implantation; results per embryo transfer, not per woman |
| De Croo 2013 | Implantation rate per woman reported in the abstract. Contacted for full data; no response from study authors, so excluded |
| Demirol 2003 | No pregnancy data provided |
| Dirnfeld 2003 | No hatching |
| Dokras 1994 | No appropriate outcome measure |
| Domitrz 2000 | No clear information about randomisation and allocation |
| Ebner 2002 | No per woman data |
| Edirisinghe 1999 | Not randomised |
| Feng 2009 | Not a prospective study ‐ a retrospective study |
| Figueira 2012 | Implantation and pregnancy rates provided in percentages. Date per embryo transfer. Not enough data to utilise study. Study population egg donation cryobank programme, which was not the reason for exclusion |
| Frydman 2006 | No per woman data |
| Gabrielsen 2004 | Pseudo‐randomised (alternate days) |
| Grace 2007 | No control. Comparing assisted hatching in good embryos with assisted hatching in poor embryos |
| Hershlag 1999 | Not randomised Control group from the period 1990 to 1993; assisted hatching group from 1994 to 1996 (historical controls) |
| Hiraoka 2009 | No control. Comparing half thinning vs quarter thinning |
| Hur 2011 | Not clear whether randomised; results appear to be per embryo transfer rather than per woman |
| Huttelova 1999 | Not randomised Benefits of AH confounded by concurrent assessment of 2 different culture media |
| Kanyo 2016 | Quasi‐randomisation. Randomised based on last number/digit of registration number given by administrator at the reception desk at first visit to the centre; study authors contacted but no further details obtained; therefore decision to exclude |
| Kirienko 2019 | Included cycles with donor oocytes; contacted to see whether could provide separate data for donor/autologous cycles – no reply |
| Komarovsky 2002 | No per woman data |
| Komarovsky 2003 | No per woman data |
| Le 2018 | No control arm; this is an RCT of thinning assisted hatching vs drilling assisted hatching of ZP before FET |
| Lee 1999 | Not randomised |
| Levron 2003 | No per woman data |
| Lu 2016 | Quasi‐randomised study |
| Lu 2019 | Full article demonstrated this was a retrospective study ‐ not an RCT |
| Ma 2007 | No per woman data |
| Magli 1998 | No per woman data |
| Mahadevan 1998 | Not randomised No concurrent controls |
| Mansour 2000 | Randomisation by alternate day ‐ inadequate allocation |
| Meldrum 1998 | Not randomised No concurrent controls |
| Montag 1999 | Not randomised No concurrent controls |
| Nadir 2005 | Alternate randomisation. |
| Nagy 2003 | No per woman data |
| Nakayama 1998 | No appropriate outcome measure |
| Nakayama 1999 | No per woman data |
| NCT02124291 | Study terminated for insufficient enrolment, (only 18 patients enrolled); no data available |
| Ng 2008 | No control. Compared 2 methods of laser |
| Obradors 2012 | Vitrified embryos from oocyte donation programme |
| Obruca 1994 | Not randomised No concurrent controls |
| Olivennes 1997 | No per woman data |
| Peterson 2006 | Results per embryo transfer only No per woman data |
| Ren 2013 | Study looked at effects of the site of assisted hatching on embryo comparing performing AH at the site near inner cell mass (ICM) vs performing AH at the site opposite to the ICM; there was no control group with no AH |
| Rienzi 2002 | Assisted hatching was part of the ICSI method |
| Ringler 1999 | Not clear how many women were included in the study or for how many cycles (only cycles were mentioned); mixture of participants and donated eggs was used for the study |
| Schoolcraft 1994 | Not randomised Control and intervention groups recruited at different times |
| Shahin 2003 | No per woman data |
| Sifer 2005 | Per cycle data only No per woman data |
| Szell 1998 | Not randomised Benefits of assisted hatching confounded by concurrent assessment of 2 different culture media |
| Tao 1997 | Not randomised Some of the women in the assisted hatching group were randomised but most were allocated to assisted hatching routinely, with no control option |
| Tucker 1991 | Not randomised |
| Urman 2002 | Inadequate method of allocation |
| Valojerdi 2008 | Inadequate method of allocation |
| Yano 2007 | No per woman data, only per cycle data |
| Zech 1998 | Numbers in tables do not add up correctly and text and tables are contradictory on age groups used in the prospective part of the study. Asked for clarification from authors ‐ no response |
| Zhang 2009 | Not a prospective study ‐ retrospective study |
AH: assisted hatching. FET: fresh embryo transfer. hCG: human chorionic gonadotropin. ICM: inner cell mass. ICSI: intracytoplasmic sperm injection. RCT: randomised controlled trial. ZP: zona pellucida.