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Table 4 Meta-analysis of the association between various birth size measurements and percent breast density, stratified by potential sources of between-study heterogeneity

From: Pre-natal exposures and breast tissue composition: findings from a British pre-birth cohort of young women and a systematic review

Perinatal factor Number of studiesa Average relative changeb (95 % CI) z-score p value I 2 statistic (%) References
Birth size measurements:
 Birthweight
  Overallc 9 1.59 (1.58–1.59) <0.001 100.0 [21, 22, 25, 26, 33, 35, 49, 50]; present study
  Using Andersen et al. [35] OR2d 9 1.59 (1.58–1.59) <0.001 100.0
  Excluding present study 8 1.63 (1.62–1.63) <0.001 100.0
 Menopausal status
  Pre-menopausal women 3 1.03 (1.02–1.04) <0.001 38.1 [21, 22]; present study
  Post-menopausal women 3 1.72 (1.71–1.72) <0.001 99.7 [21, 22, 26]
 Source of birthweight data
  Self-/parent report 4 0.99 (0.99–1.00) 0.117 91.0 [21, 22, 35, 50]
  Hospital records 5 1.67 (1.66–1.67) <0.001 10.0 [25, 26, 33, 49] present study
 Breast density assessment method
  Radiographer-assessed 4 1.05 (1.00–1.10) 0.066 49.7 [25, 33, 35, 49]
  Computer-assisted 5 1.59 (1.58–1.59) <0.001 100.0 [21, 22, 26, 50] present study
 Restricted to hospital records
  Radiographer-assessed 3 1.07 (1.02–1.13) 0.013 33.3 [25, 33, 49]
  Computer-assisted 2 1.67 (1.66–1.67) <0.001 100.0 [26]; present study
 Quality scoree
  Highest tertile (≥50) 3 1.67 (1.66–1.67) <0.001 100.0 [26, 35]; present study
  Middle tertile (40–50) 3 0.99 (0.99–1.00) 0.142 94.7 [22, 48, 50]
  Lowest tertile (<40) 3 1.04 (0.99–1.09) 0.160 26.3 [21, 25, 35]
 Birth length
  Overall 3 1.02 (1.00–1.04) 0.051 89.2 [25, 26]; present study
 Head circumference
  Overall 2 1.11 (1.11–1.11) <0.001 100.0 [26]; present study
 Maternal age
  Overall 5 1.01 (1.01–1.02) <0.001 31.7 [20, 22, 25, 50]; present study
  Excluding present study 4 1.01 (1.01–1.02) <0.001 21.9  
  Menopausal status
   Pre-menopausal women 3 1.00 (0.99–1.02) 0.539 0.0 [20, 22]; present study
   Post-menopausal women 3 1.01 (1.01–1.02) <0.001 0.0 [20, 22, 50]
  Quality score (maximum 59)d
   Highest (≥40) 3 1.01 (1.01–1.02) <0.001 17.4 [22, 50]; present study
   Lowest (<40) 2 1.00 (0.97–1.04) 0.898 67.2 [20, 25]
  1. aLope et al. [20] was not included in the birthweight meta-analysis, owing to concerns about the validity of a summary trend measure across the limited number of categories (three groups)
  2. bDue to the high between-study heterogeneity in most strata, these average estimates should be interpreted simply as indicators of the direction of the trend in breast density with increasing birth size
  3. cMeta-analysis uses OR1 from Andersen et al. [35] as reported in Table S3, which is adjusted for age at screening and birth cohort: OR 0.98; 95 % CI 0.90–1.07
  4. dMeta-analysis uses OR2 from Andersen et al. [35] as reported in Table S3, which is adjusted for age at screening, birth cohort and BMI at age 13 years: OR 1.11; 95 % CI 1.02–1.22
  5. eRange 0–59; see Methods section of main text and Additional file 1: Methods 3 for description of how study quality scores were developed