Comparison 3. Clinical pregnancy: assisted hatching compared with no assisted hatching.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
3.1 Clinical pregnancy rate per woman randomised	39	7249	Odds Ratio (M‐H, Fixed, 95% CI)	1.20 [1.09, 1.33]
3.2 First or repeat attempt	18		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
3.2.1 First attempt at IVF or ICSI	8	1010	Odds Ratio (M‐H, Fixed, 95% CI)	0.74 [0.56, 0.98]
3.2.2 Repeat attempt at IVF or ICSI	11	1798	Odds Ratio (M‐H, Fixed, 95% CI)	1.65 [1.34, 2.04]
3.3 Conception mode	26		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
3.3.1 ICSI only	11	1825	Odds Ratio (M‐H, Fixed, 95% CI)	1.40 [1.14, 1.71]
3.3.2 IVF only	15	2460	Odds Ratio (M‐H, Fixed, 95% CI)	1.31 [1.10, 1.55]
3.4 Hatching method	39		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
3.4.1 Chemical	11	1536	Odds Ratio (M‐H, Fixed, 95% CI)	1.33 [1.08, 1.64]
3.4.2 Laser	23	5127	Odds Ratio (M‐H, Fixed, 95% CI)	1.15 [1.03, 1.30]
3.4.3 Mechanical	5	586	Odds Ratio (M‐H, Fixed, 95% CI)	1.30 [0.89, 1.88]
3.5 Prognosis	24		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
3.5.1 Poor prognosis	14	2108	Odds Ratio (M‐H, Fixed, 95% CI)	1.68 [1.38, 2.04]
3.5.2 Good prognosis	14	2721	Odds Ratio (M‐H, Fixed, 95% CI)	1.10 [0.94, 1.29]
3.6 Extent of assisted hatching	37		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
3.6.1 Thinning only	17	3774	Odds Ratio (M‐H, Fixed, 95% CI)	1.10 [0.96, 1.26]
3.6.2 Breach by hole only	17	2543	Odds Ratio (M‐H, Fixed, 95% CI)	1.17 [0.98, 1.39]
3.6.3 Complete removal of zona	2	301	Odds Ratio (M‐H, Fixed, 95% CI)	1.93 [1.21, 3.09]
3.6.4 Expansion of zona pellucida	1	125	Odds Ratio (M‐H, Fixed, 95% CI)	2.37 [1.07, 5.28]
3.7 Fresh and frozen embryo transfer	38		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
3.7.1 Fresh embryo transfer	30	5349	Odds Ratio (M‐H, Fixed, 95% CI)	1.23 [1.10, 1.38]
3.7.2 Frozen embryo transfer only	10	1700	Odds Ratio (M‐H, Fixed, 95% CI)	1.15 [0.93, 1.42]