Background: Failure of implantation and conception may result from an inability of the blastocyst to escape from its outer coat, known as the zona pellucida. Artificial disruption of this coat is known as assisted hatching (AH) and has been proposed as a method for improving the success of assisted conception.
Objectives: To determine whether assisted hatching (AH) of embryos facilitates live births and clinical pregnancy.
Search strategy: We previously searched the Cochrane Menstrual Disorders and Subfertility Group Specialsed Register (February 2007), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2007), MEDLINE (1966 to February 2007) and EMBASE (1980 to February 2007).
Selection criteria: Two authors identified and independently screened trials. We included randomised controlled trials (RCTs) of AH (mechanical, chemical or laser disruption of the zona pellucida prior to embryo replacement) versus no AH, which reported live birth or clinical pregnancy rates.
Data collection and analysis: Two authors independently performed qualitative assessments and data extraction.
Main results: Twenty-eight trials reported clinical pregnancy data, including 1228 clinical pregnancies in 3646 women. There was no significant difference in the odds of live births in the AH compared with control groups (seven RCTs; OR 1.13, 95% CI 0.83 to 1.55; 255 births from 719 women, with no heterogeneity (P = 0.37) or inconsistency I(2) = 8%)). We also analysed the clinical pregnancy rate from the seven studies that reported live births, which was non-significant (OR 1.13, 95% CI 0.83 to 1.54). Inclusion of studies which were more robust in methodology showed an increase in clinical pregnancy rate which was just statistically significant (16 RCTs; OR 1.20, 95% CI 1.00 to 1.45, P = 0.05). Analysis of all the studies included in this update (28 RCTs) showed a marked increase in clinical pregnancy rate (OR 1.29, 95% CI 1.12 to 1.49).Miscarriage rates per women were similar in both groups (14 RCTs; OR 1.13, 95% CI 0.74 to 1.73). Multiple pregnancy rates per woman were significantly increased in women who were randomised to AH compared with women in control groups (12 RCTs; OR 1.67, 95% CI 1.24 to 2.26).
Authors' conclusions: The improvement in clinical pregnancy rate (CPR) with AH means that a clinic with a success rate of 25% could anticipate improving the CPR to between 29% and 49%, all things being equal. The included trials provided insufficient data to investigate the impact of assisted hatching on several important outcomes.