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Table 2 Results from weighted Cox regression analysis

From: Parity and breast cancer risk among BRCA1 and BRCA2mutation carriers

Parameter All BRCA1 carriers BRCA2 carriers
  UN BC HR 95% CI UN BC HR 95% CI UN BC HR 95% CI
Parity             
   Nulliparous 37 65 1.00   25 37 1.00   12 28 1.00  
   Parous 295 392 0.54 0.37–0.81 193 211 0.53 0.34–0.83 102 181 0.58 0.27–1.24
Parity by attained age             
   ≤40 years             
Nulliparous 28 44 1.00   21 24 1.00   7 20 1.00  
Parousa 76 127 1.01 0.58–1.76 50 76 1.17 0.55–2.52 26 51 0.72 0.42–1.24
   >40 years             
Nulliparous 9 21 1.00   4 13 1.00   5 8 1.00  
Parous 219 265 0.44 0.23–0.84 143 135 0.34 0.16–0.70 76 130 1.21 0.37–3.92
Number of live birthsb             
   Nulliparous 37 65 1.00   25 37 1.00   12 28 1.00  
   1 46 57 0.62 0.37–1.02 27 34 0.62 0.34–1.11 19 23 0.58 0.22–1.53
   2 109 167 0.57 0.38–0.86 73 80 0.54 0.33–0.87 36 87 0.68 0.31–1.47
   3 66 79 0.64 0.34–0.86 42 50 0.56 0.33–0.97 24 29 0.44 0.19–1.04
   4+ 56 82 0.55 0.34–0.91 42 44 0.51 0.29–0.89 14 38 0.71 0.27–1.88
   Per live birth    0.90 0.80–1.00    0.89 0.78–1.01    0.93 0.75–1.14
Age at first live birth             
   <20 years 61 55 1.00   38 35 1.00   23 20 1.00  
   20–24 years 132 179 1.16 0.76–1.78 85 92 1.08 0.65–1.78 47 87 1.74 0.87–3.49
   25–29 years 106 108 1.13 0.72–1.79 73 66 1.08 0.64–1.52 33 42 1.48 0.68–3.22
   ≥ 30 years 39 50 1.30 0.74–2.29 25 18 0.83 0.42–1.64 14 32 4.77 2.08–10.94
   Nulliparous 37 65 2.09 1.26–3.45 25 37 1.96 1.10–3.52 12 28 2.85 1.13–7.15
  1. UN, unaffected carriers; BC, breast cancer; HR, hazard ratio; CI, confidence interval. aAnalyses not adjusted for oophorectomy (all others adjusted). Overall analysis stratified by year of birth and gene. bAssuming that births between first and last birth were equally spaced; 25 carriers (7 affected, 18 unaffected) with missing age at last birth were assumed to be nulliparous until age at first birth and were then considered as a separate category (hazard ratios not shown).