Table 3.
Summary of subgroup analysis according to study type, quality score, potential for recall bias, and study subjects
| SGA | LBW | Infertility | Fetal death | Preterm delivery | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| N a | I 2 (%) | Model | Summary OR (95 % CI) | N | I 2 (%) | Model | Summary OR (95 % CI) | N | I 2 (%) | Model | Summary OR (95 % CI) | N | I 2 (%) | Model | Summary OR (95 % CI) | N | I 2 (%) | Model | Summary OR (95 % CI) | |
| Total | 7 | 87.15 | RE | 1.14 (0.97–1.33) | 8 | 72.36 | RE | 1.12 (0.98–1.27) | 6 | 42.71 | FE | 1.15* (1.03–1.28) | 9 | 20.64 | FE | 1.14* (1.04–1.24) | 8 | 0 | FE | 1.04* (1.00–1.07) |
| Study type | ||||||||||||||||||||
| Registry-based | 7 | 87.15 | RE | 1.14 (0.97–1.33) | 5 | 81.03 | RE | 1.11 (0.97–1.27) | 1 | NA | 3 | 53.34 | RE | 1.12 (0.79–1.59) | 5 | 0 | FE | 1.04* (1.00–1.07) | ||
| Questionnaire-based | 0 | NA | 3 | 45.52 | FE | 1.17 (0.88–1.56) | 5 | 47.21 | FE | 1.18* (1.05–1.32) | 6 | 6.83 | FE | 1.16* (1.04–1.29) | 3 | 0 | FE | 0.91 (0.72–1.16) | ||
| Quality score | ||||||||||||||||||||
| ≥7 | 6 | 86.73 | RE | 1.12 (0.92–1.36) | 6 | 78.66 | RE | 1.10 (0.89–1.35) | 3 | 21.00 | FE | 1.17 (0.99–1.38) | 7 | 13.06 | FE | 1.12 (0.99–1.27) | 7 | 0 | FE | 1.03* (1.00–1.07) |
| <7 | 1 | NA | 2 | NA | 3 | 67.18 | RE | 1.06 (0.82–1.38) | 2 | NA | 1 | NA | ||||||||
| Potential for recall bias | ||||||||||||||||||||
| Low | 7 | 87.15 | RE | 1.14 (0.97–1.33) | 6 | 77.55 | RE | 1.12 (0.98–1.29) | 1 | NA | 4 | 50.51 | RE | 1.20 (0.89–1.64) | 6 | 0 | FE | 1.04* (1.00–1.07) | ||
| High | 0 | NA | 2 | NA | 5 | 47.21 | FE | 1.18* (1.05–1.32) | 5 | 0 | FE | 1.14* (1.02–1.28) | 2 | NA | ||||||
| Study subjectsb | ||||||||||||||||||||
| Hairdresser | 5 | 69.47 | RE | 1.20* (1.00–1.45) | 6 | 57.41 | RE | 1.20* (1.03–1.40) | 5 | 20.48 | FE | 1.19* (1.06–1.32) | 7 | 33.71 | FE | 1.13* (1.03–1.25) | 5 | 0 | FE | 1.09* (1.02–1.16) |
| Cosmetologist | 3 | 78.30 | RE | 1.11 (0.91–1.35) | 3 | 41.94 | FE | 1.00 (0.96–1.05) | 1 | NA | 3 | 0 | FE | 1.15 (0.88–1.49) | 4 | 33.88 | FE | 1.02 (0.98–1.06) | ||
OR odds ratio, CI confidence interval, SGA small for gestational age, LBW low birth weight, RE random-effect model, FE fixed-effect model, NA not available
* Statistical significance
aNumber of included studies
bThe study by Halliday-Bell et al. (2009) was evaluated as two separate studies