Comparison 2. Multiple pregnancy: assisted hatching compared with no assisted hatching.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
2.1 Multiple pregnancy rate per woman randomised	18	4308	Odds Ratio (M‐H, Fixed, 95% CI)	1.38 [1.13, 1.68]
2.2 First or repeat attempt	8		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
2.2.1 First attempt at IVF or ICSI	4	654	Odds Ratio (M‐H, Fixed, 95% CI)	0.73 [0.31, 1.72]
2.2.2 Repeat attempt at IVF or ICSI	5	1068	Odds Ratio (M‐H, Fixed, 95% CI)	1.25 [0.80, 1.94]
2.3 Conception mode	9		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
2.3.1 ICSI only	3	573	Odds Ratio (M‐H, Fixed, 95% CI)	3.09 [1.57, 6.08]
2.3.2 IVF only	6	1126	Odds Ratio (M‐H, Fixed, 95% CI)	1.87 [1.28, 2.72]
2.4 Hatching method	18		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
2.4.1 Chemical	4	534	Odds Ratio (M‐H, Fixed, 95% CI)	1.55 [0.98, 2.47]
2.4.2 Laser	13	3730	Odds Ratio (M‐H, Fixed, 95% CI)	1.29 [1.03, 1.61]
2.4.3 Mechanical	1	44	Odds Ratio (M‐H, Fixed, 95% CI)	8.33 [1.56, 44.64]
2.5 Prognosis	10		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
2.5.1 Poor prognosis	6	1186	Odds Ratio (M‐H, Fixed, 95% CI)	1.95 [1.27, 3.00]
2.5.2 Good prognosis	6	1569	Odds Ratio (M‐H, Fixed, 95% CI)	1.08 [0.81, 1.44]
2.6 Multiple pregnancy rate per woman grouped by extent of assisted hatching	16		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only
2.6.1 Thinning only	6	2148	Odds Ratio (M‐H, Fixed, 95% CI)	1.34 [1.02, 1.76]
2.6.2 Breach by hole	9	1629	Odds Ratio (M‐H, Fixed, 95% CI)	1.51 [1.08, 2.11]
2.6.3 Complete removal of zona	1	25	Odds Ratio (M‐H, Fixed, 95% CI)	0.62 [0.07, 5.28]
2.7 Fresh or frozen embryo transfer	16	3190	Odds Ratio (M‐H, Fixed, 95% CI)	1.38 [1.08, 1.75]
2.7.1 Fresh	13	2264	Odds Ratio (M‐H, Fixed, 95% CI)	1.30 [0.98, 1.73]
2.7.2 Frozen	3	926	Odds Ratio (M‐H, Fixed, 95% CI)	1.60 [1.00, 2.55]
2.8 Multiple pregnancy per pregnancy	17	1598	Odds Ratio (M‐H, Fixed, 95% CI)	1.37 [1.09, 1.72]