Table 2. Heterogeneity test and meta analysis results.
| Risk Factor | reference group | Number of studies | Heterogeneity | Pooling Model | Meta-analysis results | |||
|---|---|---|---|---|---|---|---|---|
| P-value | I2 (%) | OR (95%CI) | P-value | |||||
| EMT on HCG day | Thin | Thick | 14 | <0.001 | 71.2 | Random | 1.951 (1.598–2.381) | <0.001 |
| History of EP | Yes | No | 14 | <0.001 | 79.3 | Random | 1.541 (1.213–1.957) | <0.001 |
| Infertility type | Secondary | Primary | 8 | 0.083 | 44.4 | Fixed | 1.326 (1.171–1.502) | <0.001 |
| EMT at transplantation | Thin | Thick | 5 | 0.049 | 58.1 | Random | 1.511 (1.197–1.908) | 0.001 |
| Previous miscarriage | Yes | No | 3 | 0.937 | 0 | Fixed | 2.054 (1.310–3.222) | 0.002 |
| PCOS | Yes | No | 3 | 0.377 | 0 | Fixed | 2.164 (1.386–3.381) | 0.001 |
| Male factor infertility | Yes | No | 3 | 0.078 | 60.9 | Random | 0.534 (0.342–0.834) | 0.006 |
| DOR | Yes | No | 2 | 0.359 | 0 | Fixed | 1.751 (1.346–2.279) | <0.001 |
| Tubal factor infertility | Yes | No | 17 | 0.001 | 59.3 | Random | 1.851 (1.609–2.130) | <0.001 |
| Embryo transfer stage | Cleavage | Blastocyst | 12 | <0.001 | 83.1 | Random | 1.870 (1.417–2.466) | <0.001 |
| Type of transfer | Fresh | Frozen | 8 | <0.001 | 88.5 | Random | 1.463 (1.062–2.016) | 0.020 |
| Endometrial preparation | Artificial | Natural | 4 | 0.756 | 0 | Fixed | 2.067 (1.718–2.487) | <0.001 |
| E2 level on HCG day | High | Low | 3 | 0.192 | 39.4 | Fixed | 1.001 (1.001–1.001) | <0.001 |
| Previous tubal surgery | Yes | No | 7 | 0.478 | 0 | Fixed | 2.692 (2.075–3.494) | <0.001 |
| Maternal age | ≥30 | <30 | 4 | 0.002 | 79.7 | Random | 0.935 (0.880–0.993) | 0.029 |
| No. of transferred embryos | ≥2 | <2 | 10 | 0.003 | 63.8 | Random | 1.517 (1.226–1.878) | <0.001 |
| Fertilization method | IVF | ICSI | 4 | 0.043 | 63.2 | Random | 1.122 (0.734–1.715) | 0.595 |
| Previous of cesarean section | Yes | No | 3 | 0.338 | 7.8 | Fixed | 1.632 (1.005–2.652) | 0.048 |
| Ovulation Protocol | Antagonist | Agonist | 4 | 0.021 | 69.1 | Random | 1.193 (0.677–2.102) | 0.542 |
| No. of oocytes retrieved | - | - | 2 | 0.385 | 0 | Fixed | 1.020 (0.994–1.047) | 0.138 |
| Maternal BMI | - | - | 4 | 0.765 | 0 | Fixed | 1.001 (1.000–1.002) | 0.056 |
| Previous pregnancy | Yes | No | 3 | 0.297 | 17.7 | Fixed | 1.227 (1.057–1.423) | 0.007 |
| History of pelvic surgery | Yes | No | 7 | 0.005 | 67.5 | Random | 1.909 (1.349–2.701) | <0.001 |
| Dose of gonadotrophin (IU) | - | - | 4 | 0.657 | 0 | Fixed | 1.530 (0.940–2.490) | 0.087 |
EMT:endometrial thickness; HCG:human chorionic gonadotropin; EP:ectopic pregnancy; PCOS:polycystic ovarian syndrome; DOR:diminished ovarian reserve; E2:estradiol; BMI:body mass index.