Table 1

Characteristics of breast cancer cases and controls at index pregnancy

Cases (%) (n = 194)Controls (%) (n = 374)ORa (95% CI)
Age (yrs)
 ≤206.25.41.0
 21–2515.517.40.81 (0.35–1.9)
 26–3024.723.51.5 (0.65–3.2)
 31–3528.427.52.6 (1.2–5.8)
 ≥3625.326.23.2 (1.5–7.1)
Race
 White60.866.31.0
 Black28.423.01.3 (0.89–2.0)
 Other10.810.71.1 (0.63–2.0)
Age at first pregnancy (yrs)
 ≤2019.126.71.0
 21–2539.241.21.3 (0.81–2.1)
 26–3028.421.91.9 (1.1–3.2)
 ≥3113.410.22.1 (1.1–4.1)
Previous pregnancies
 021.119.81.0
 126.323.51.0 (0.60–1.7)
 227.321.71.1 (0.65–2.0)
 ≥325.335.00.57 (0.32–1.0)
Age at menarche (yrs)
 ≤1116.513.61.0
 1222.721.70.85 (0.48–1.5)
 1322.217.90.99 (0.55–1.8)
 ≥1413.917.10.70 (0.37–1.3)
 Missing24.729.7
Prepregnancy body mass index (kg/m2)
 <2018.618.51.0
 20–2447.447.91.0 (0.64–1.7)
 25–2911.312.30.95 (0.49–1.8)
 ≥304.13.21.2 (0.46–3.4)
 Missing18.618.2
Smoking (cigarettes/day)
 Nonsmokers/past smokers68.068.51.0
 1–912.49.61.3 (0.78–2.4)
 10–197.76.71.2 (0.59–2.3)
 ≥2011.914.20.82 (0.48–1.4)
 Missing0.01.1
Alcohol (drinks/wk)
 Nondrinkers42.348.91.0
 1–3.525.821.71.4 (0.93–2.2)
 ≥416.015.01.2 (0.72–2.0)
 Missing16.014.4
Caffeine (cups/day)
 <115.515.81.0
 1–337.635.81.1 (0.63–1.8)
 4–616.522.70.80 (0.43–1.5)
 >616.012.81.3 (0.68–2.6)
 Missing14.412.8
  • a ORs for all variables except age were adjusted for the matching factor, age at index pregnancy.