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Table 5 Table 5 Studies assessing the association of premature birth and the risk of breast cancer

From: Intrauterine environments and breast cancer risk: meta-analysis and systematic review

Type of study Author Year Design Cases Controls (or cohort) Country/place of study Gestational age (weeks) OR (95% CI) Comments
Case-control studies [42]a 1988 PCC 153 461 USA 25–32 1.16 (0.50–1.54) Matched analysis
        33–40 Referent  
  [13]b 1996 NCC 571 1,525 USA Categorical   Adjusted for age
           40 Referent  
           38–39 0.76 (0.44–1.32)  
           36–37 0.96 (0.59–1.56)  
        Binomial   
           ≥ 37 Referent  
           ≤ 36 0.82 (0.37–1.82)  
  [14] 1996 PCC 1123 1371 USA Nonpreterm Referent Adjusted for age, menopausal status, and maternal smoking
        Preterm 1.1 (0.5–2.1)  
  [32]a 1997 NCC 1,010 2,625 Sweden ≥ 33 Referent Adjusted for maternal age, matermal socioeconomic status, maternal parity, maternal pre-eclampsia or eclampsia, neonatal jaundice, severe prematurity, twin, and birth weight
        ≤ 32 3.96 (1.46–10.81)  
  [33]b 1998 PCC 502 433 USA ≥ 43 1.5 (0.8–2.6) Crude ORs
        37–42 Referent  
        ≤ 36 0.9 (0.5–1.8)  
  [15]a,b 2000 LCC 480 2,854 USA ≥ 37 Referent Crude ORs
        33–36 1.34 (0.85–2.13)  
        ≤ 32 0.55 (0.19–1.57)  
  [34]a,b 2001 LCC 87 87 Sweden ≥ 40 8.4 (1.3–54.4) Matched analysis by conditional logistic regression
        37–40 3.4 (0.7–17.0)  
        33–36 3.5 (0.7–17.5)  
        ≤ 32 Referent  
  [25]a 2003 LCohort 127 (1,483) Sweden ≥ 33 1.08 (0.64–1.70) Standardized incidence ratio (expected/observed)
        ≤ 32 0.92 (0.57–1.41)  
  [45]a,b 2004 LCC 2,471 9,801 USA ≥ 37 Referent Adjusted for age and maternal age at first birth
        32–36 0.91 (0.72–1.13)  
        ≤ 31 1.43 (0.90–2.28)  
  [20]b 2005 PCC 1,424 1,457 Poland ≥ 37 Referent Adjusted for age, education, age at menarche, menopausal status and age at menopause, age at first full-term pregnancy, number of full-term pregnancies, family history of breast cancer among first-degree relatives, mammography screening, and current body mass index
        ≤ 36 1.01 (0.75–1.32)  
Cohort studies [62]c 2000 LCohort 12 273 Sweden 35 0.2 (0.01–1.3) Standardized incidence ratio
        33–34 0.7 (0.1–2.0)  
        31–32 2.3 (0.7–5.3)  
        <31 6.7 (1.4–19.5)  
  [16]c 2001 LTCCS 2,265 9,060 Sweden 33–36 Referent Crude ORs
        37–38 1.8 (0.83–4.0)  
        40–44 2.0 (0.88–4.6)  
  [29]c 2005 LCohort 367 5,346 Sweden 1 week increase <50 years  
         0.94 (0.83–1.07)  
  [40]c 2006 Cohort 97 5,847 USA <39 0.77 (0.42–1.4) Adjusted for age
        39 1.38 (0.78–2.4)  
        40 Referent  
        41+ 1.33 (0.67–2.6)  
  [31]b 2006 Cohort 249 1024 USA ≥ 43 0.7 (0.2–2.7) Adjusted for: age at diagnosis, diagnosis year, stage at diagnosis, and birth order, with exception of birth order, which is adjusted for maternal age
        37–42 Referent  
        <37 1.4 (0.7–2.9)  
         P for trend = 0.3  
  1. Cohort, cohort study; LCC, case-control study with linkage with population and cancer registry data; LTCCS, twin case-control study by using linkage with birth and cancer registry data; NCC, nested case-control study in cohort; PCC, population-based case-control study. aWe included this study in the meta-analysis with categories of ≥33 versus ≤32 months (reference). bWe included this study in the meta-analysis with categories of ≥37 versus ≤36 months (reference). cWe did not include these studies in the meta-analysis because they employed different categories or a continuous scale, or they did not provide the numbers of cases and controls in the report.