Table 2. Stratified analysis of the associations of MTHFR C677T polymorphism with H and HIP under dominant model.
| H & HIP | H | HIP | |||||||
| Subgroup analysis | n | OR (95% CI) | P h (I2%) | n | OR (95% CI) | P h (I2%) | n | OR (95% CI) | P h (I2%) |
| All HWE | 81 | 1.23 (1.13–1.34) | <0.001 (44.9) | 28 | 1.35 (1.17–1.54) | <0.001 (51.0) | 53 | 1.16 (1.05–1.28) | 0.003 (38.7) |
| Ethnicity | |||||||||
| East Asians | 40 | 1.46 (1.29–1.66) | <0.001 (55.7) | 23 | 1.38 (1.19–1.60) | <0.001 (55.5) | 17 | 1.64 (1.28–2.10) | 0.002 (57.6) |
| Caucasians | 43 | 1.18 (1.07–1.29) | 0.116 (21.0) | 10 | 1.29 (1.01–1.63) | 0.004 (62.5) | 33 | 1.15 (1.05–1.26) | 0.648 (0.00) |
| Latinos | 10 | 1.09 (0.86–1.39) | 0.098 (38.9) | 1 | 1.43 (0.81–2.51) | – | 9 | 1.06 (0.82–1.37) | 0.094(41.0) |
| Indians and | 5 | 0.93 (0.56–1.56) | 0.004 (74.4) | 1 | 1.71 (1.00–2.91) | – | 4 | 0.78 (0.48–1.29) | 0.039 (64.2) |
| Sri Lankans | |||||||||
| Black Africans | 3 | 1.22 (0.89–1.67) | 0.513 (0.00) | 0 | – | – | 3 | 1.22 (0.89–1.67) | 0.513 (0.0) |
| Source of controls | |||||||||
| Hospital based | 80 | 1.30 (1.18–1.43) | <0.001 (51.0) | 23 | 1.51 (1.30–1.75) | 0.003 (50.5) | 57 | 1.20 (1.07–1.35) | <0.001 (46.8) |
| Population based | 21 | 1.19 (1.06–1.34) | 0.048 (36.4) | 12 | 1.15 (0.95–1.40) | 0.005 (59.3) | 9 | 1.22 (1.08–1.42) | 0.808 (0.0) |
| Genotyping methods | |||||||||
| PCR-RFLP | 86 | 1.28 (1.18–1.40) | <0.001 (50.4) | 31 | 1.36 (1.20–1.54) | <0.001 (57.6) | 55 | 1.23 (1.10–1.38) | <0.001 (44.5) |
| Others | 15 | 1.16 (1.02–1.32) | 0.122 (30.9) | 4 | 1.40 (1.01–1.96) | 0.213 (33.2) | 11 | 1.08(0.93–1.26) | 0.262 (19.1) |
| Sample size | |||||||||
| Large (≥225) | 51 | 1.17 (1.07–1.27) | <0.001 (54.0) | 25 | 1.30 (1.14–1.48) | <0.001 (58.6) | 26 | 1.05 (0.94–1.17) | 0.033 (36.7) |
| Small (<225) | 50 | 1.46 (1.28–1.67) | 0.014 (33.2) | 10 | 1.63 (1.31–2.04) | 0.154 (33.0) | 40 | 1.41 (1.21–1.63) | 0.025 (32.8) |
| Study quality | |||||||||
| High (≥5 scores) | 89 | 1.25 (1.15–1.36) | <0.001 (49.2) | 31 | 1.34 (1.18–1.52) | <0.001 (55.9) | 58 | 1.19 (1.07–1.32) | <0.001 (42.8) |
| Low (<5 scores) | 12 | 1.34 (1.06–1.70) | 0.063 (41.8) | 4 | 1.58 (1.03–2.42) | 0.086 (54.6) | 8 | 1.23 (1.01–1.64) | 0.135 (36.8) |
Abbreviation: MTHFR, methylenetetrahydrofolate reductase; HWE, Hardy-Weinberg equilibrium; H, hypertension; HIP, hypertension in pregnancy; OR, odds ratio; CI, confidence interval; P h, P value for heterogeneity test; n, the number of studies; PCR-RFLP, polymerase chain reaction-restriction fragment length polymorphism.