Table 1.
Summary data on the association between early life exposures and IBD on meta-analyses.
| Exposure category | Exposure analyzed | Number of studies meta-analyzed | Type of study | Outcome | Pooled estimate | 95% CI | I² (%) | P value for heterogeneity test |
|---|---|---|---|---|---|---|---|---|
| Maternal health and exposures during pregnancy | Maternal smoking | 9 | CC, cohort | IBD | 1.491 | 1.171–1.898 | 72.04 | <0.001 |
| Maternal smoking | 6 | CC | CD | 1.208 | 0.747–1.956 | 83.55 | <0.001 | |
| Maternal smoking | 4 | CC | UC | 1.511 | 0.990–2.306 | 68.05 | 0.025 | |
| Maternal age | 4 | CC, cohort | IBD | 0.863 | 0.452–1.648 | 87.05 | <0.001 | |
| Maternal age | 2 | Cohort | CD | 0.773 | 0.219–2.726 | 95.27 | <0.001 | |
| Antibiotics | 2 | Cohort | IBD | 1.751 | 1.222–2.510 | 0 | 0.62 | |
| Perinatal factors | Birth weight | 10 | CC, cohort | IBD | 0.92 | 0.727–1.164 | 76.75 | <0.001 |
| Birth weight | 6 | CC, cohort | CD | 0.875 | 0.624–1.225 | 70.72 | 0.004 | |
| Birth weight | 3 | CC, cohort | UC | 0.831 | 0.412–1.677 | 81.66 | 0.004 | |
| Premature birth | 8 | CC, cohort | IBD | 1.055 | 0.933–1.194 | 0 | 0.49 | |
| Premature birth | 5 | CC, cohort | CD | 1.073 | 0.890–1.293 | 5.33 | 0.38 | |
| Premature birth | 5 | CC, cohort | UC | 1.024 | 0.669–1.570 | 53.57 | 0.07 | |
| Hygiene factors | Rural vs. urban | 7 | CC | IBD | 1.033 | 0.814–1.311 | 52.76 | 0.048 |
| Rural vs. urban | 3 | CC | CD | 1.15 | 0.668–1.979 | 68.81 | 0.041 | |
| Rural vs. urban | 4 | CC | UC | 1.053 | 0.843–1.315 | 38.33 | 0.18 | |
| Antibiotics and other medications | Antibiotics in first year | 3 | CC, cohort | IBD | 1.683 | 0.965–2.936 | 55.38 | 0.11 |
| Antibiotics in first year | 2 | CC, cohort | CD | 1.19 | 0.512–2.765 | 49.29 | 0.16 | |
| Antibiotics in first year | 2 | CC, cohort | UC | 0.925 | 0.464–1.845 | 0 | 0.49 | |
| Child health and infections | Passive smoking | 3 | CC | CD | 1.084 | 0.951–1.207 | 0 | 0.64 |
| Measles vaccine | 12 | CC | IBD | 1.078 | 0.911–1.275 | 55.52 | 0.004 | |
| Measles vaccine | 9 | CC | CD | 1.06 | 0.822–1.366 | 64.69 | 0.004 | |
| Measles vaccine | 6 | CC | UC | 1.046 | 0.844–1.296 | 28.20 | 0.22 | |
| BCG vaccine | 4 | CC | IBD | 1.549 | 0.969–2.477 | 37.58 | 0.19 | |
| BCG vaccine | 3 | CC | CD | 1.773 | 0.846–3.714 | 53.17 | 0.12 | |
| Otitis media | 2 | CC | IBD | 2.105 | 1.224–3.619 | 36.85 | 0.21 | |
| Otitis media | 2 | CC | CD | 1.947 | 1.198–3.166 | 4.41 | 0.31 |
Abbreviations: CI = confidence interval; CC = case-control; IBD = inflammatory bowel disease; CD = Crohn's disease; UC = ulcerative colitis; BCG = Bacillus Calmette–Guérin.