Table 4.

Subgroup analysis of melatonin concentration in culture media.

Outcome	Variable (melatonin concentration)	Number of studies	OR (95% CI)	p value	I 2%	Q statistics (p)
CR	Low	8	0.96 (0.78, 1.20)	0.738	36.0	0.142
	Moderate	6	1.172 (0.88, 1.56)	0.279	48.2	0.0607
	High	2	0.96 (0.67, 1.38)	0.834	0.0	0.496
BR	Low	11	1.26 (1.07, 1.49)	0.007	36.3	0.109
	Moderate	10	1.44 (1.15, 1.79)	0.001	54.4	0.020
	High	4	0.41 (0.17, 1.01)	0.052	85.4	0.00
HBR	Low	8	1.54 (1.12, 2.14)	0.009	27.8	0.206
	Moderate	6	1.57 (1.17, 2.11)	0.003	0.00	0.715
	High	4	0.54 (0.22, 1.32)	0.178	65.3	0.034

Abbreviations: BR, blastocyst rate; CR, cleavage rate; HBR, hatched-blastocyst rate; I², heterogeneity; OR, odds ratio.