• E C O Edi-Osagie, L Hooper, P McGinlay, and M W Seif.
• Cochrane Db Syst Rev. 2003 Jan 1 (4): CD001894.

BackgroundFailure of implantation and thus conception might result from inability of the blastocyst to escape from its zona pellucida. Artificial disruption of this coat has been proposed as a method of improving the success of assisted conception.ObjectivesTo determine whether assisted hatching of embryos facilitates live births, clinical pregnancy and implantation and whether it impacts on negative outcomes (such as miscarriage).Search StrategyWe searched the Cochrane Menstrual Disorders and Subfertility Group trials register (26 November 2002), the Cochrane Controlled Trials Register (Cochrane Library Issue 2, 2002), MEDLINE (1996 to February 2003), EMBASE (1980 to February 2003) 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 Authors were contacted for missing and/or unpublished data.Selection CriteriaTrials were identified and independently screened by two reviewers.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, subgrouping and meta-regression where appropriate.Main ResultsTwenty-three randomised controlled trials (2572 women) were included. There was no significant difference in the odds of live births in the AH compared with control groups (6 RCTs; OR 1.21, 95% CI 0.82 to 1.78; 161 births from 523 women). Women undergoing assisted hatching were significantly more likely to achieve clinical pregnancy (722 clinical pregnancies in 2175 women, OR 1.63, 95% CI 1.27 to 2.09), however the studies were heterogeneous. Implantation data were difficult to analyse due to the practice of replacing multiple embryos in individual women. 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.Reviewer's ConclusionsThere is insufficient evidence to determine any effect of AH on the 'take-home-baby rate' of assisted conception. There are also very few data regarding miscarriage rates and other adverse events. This prevents us from extrapolating the impact of AH on live births from our finding of improved odds of clinical pregnancy.

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