• M M W Seif, E C O Edi-Osagie, C Farquhar, L Hooper, D Blake, and P McGinlay.
• University of Manchester @ St Mary's Hospital, Academic Unit of Obstetrics, Gynaecology & Reproductive Health, Whitworth Park, Manchester, UK M13 0JH. mwseif@manchester.ac.uk
• Cochrane Db Syst Rev. 2005 Oct 19 (4): CD001894.

BackgroundFailure of implantation and conception may result from an inability of the blastocyst to escape from its outer coat, know as the zona pellucida. In vitro culture conditions and/or advancing maternal age may alter the architecture of the zona pellucida and result in hatching difficulties. Artificial disruption of this coat is known as assisted hatching (AH) has been proposed as a method of improving the success of assisted conception.ObjectivesTo determine whether assisted hatching (AH) of embryos facilitates live births and clinical pregnancy and whether it impacts on negative outcomes (such as multiple pregnancy and miscarriage).Search StrategyWe searched the Cochrane Menstrual Disorders and Subfertility Group trials register (1 June 2005), the Cochrane Controlled Trials Register (Cochrane Library Issue 2, 2005), MEDLINE (1996 to June 2003), EMBASE (1980 to June 2005) and reference lists of articles. Authors were contacted for missing and/or unpublished data.Selection CriteriaTrials were identified and independently screened by two reviewers. Randomised controlled trials of AH (mechanical, chemical or laser disruption of the zona pellucida prior to embryo replacement) versus no AH that reported live birth, clinical pregnancy or implantation rates were included.Data Collection And AnalysisQualitative assessments and data extraction were performed independently by two reviewers. Outcomes were extracted as rates and combined using random effects meta-analysis, sensitivity analysis, sub grouping and meta-regression where appropriate.Main ResultsTwenty-three randomised controlled trials consisting of 2668 women reported on 849 pregnancy outcomes. There was no significant difference in the odds of live births in the AH compared with control groups (6 RCTs; OR 1.19 95% CI 0.81 to 1.73; 163 births from 516 women). Women undergoing assisted hatching were significantly more likely to achieve clinical pregnancy (23 RCTs, OR 1.33, 95% CI 1.12 to 1.57). Miscarriage rates per woman were similar in both groups (12 RCTs OR 1.23 (95% CI 0.73 to 2.05). Multiple pregnancy rates per woman was increased in women who were randomised to AH compared with control women (9 RCTs OR 1.83 (95% CI 1.19 to 2.83). The improvement in clinical pregnancy rate means for a clinic with a success rate of 25% could anticipate improving the CPR to between 28 and 39%, all things being equal. The trials provided insufficient data to investigate the impact of assisted hatching on several important outcomes, including monozygotic twinning, embryo damage, congenital and chromosomal abnormalities, and in vitro blastocyst development.Authors' ConclusionsDespite significantly improved odds of clinical pregnancy, there is insufficient evidence to determine any effect of AH on live birth rates. The increased multiple pregnancy rate is of concern although it likely that with a policy of single embryo transfer this may be lowered. Currently, there is insufficient evidence to recommend assisted hatching.

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