Table 3 Subgroup analysis
Subgrouping criteria | No. of studies | Studies | Effect size | Heterogeneity | |||
|---|---|---|---|---|---|---|---|
RR | 95% CI | p-value | I2 (%) | p-value | |||
Use of increased NK-cell percentage (> 12%) as criterion for inclusion | 4 | Ahmadi (2019), Moraru (2012), Ramos-Medina (2014), Winger (2008) | 2.32 | [1.77, 3.02] | < 0.0001 | 0.0 | 0.413 |
No use of increased NK-cell percentage (> 12%) as criterion for inclusion | 4 | Jafarzadeh (2019), Mahmoud (2004), Perricone (2008), Stricker (2005) | 1.73 | [1.02, 2.92] | 0.041 | 75.5 | 0.007 |
Initiation of the intervention after pregnancy confirmation | 5 | Ahmadi (2019), Mahmoud (2004), Moraru (2012), Perricone (2008), Ramos-Medina (2014) | 1.71 | [1.16, 2.53] | 0.007 | 67.7 | 0.015 |
Initiation of the intervention prior to planned conception or during cycle of conception | 2 | Stricker 2005, Winger 2008 | 4.47 | [1.53, 13.05] | 0.006 | 45.2 | 0.177 |