Previous pregnancy outcome and breast density (United States)

Objective: We evaluated the association of pre-term delivery (PTD), low birth weight (LBW), and fetal death with breast density by age at mammogram and years since birth. Methods: Subjects were women aged ≤55 years who had a screening mammogram between 1 June 1996 and 1 August 1997 in Seattle, Washington, and whose records were linked to their previous state birth (1 January 1968 to 1 August 1997) or fetal death (1/1/1984–8/1/1997) records. We used unconditional logistic regression, adjusting for age at mammogram, body mass index, age at first birth, and menopausal status, to calculate the odds of dense (extremely or heterogeneously dense by BI-RADS) (n=3593) versus fatty breasts (scattered fibroglandular tissue or almost entirely fat) (n=2378) for women with a prior PTD (<34, 34–36 versus ≥37 weeks gestation), LBW (<2500 versus ≥2500 g), or fetal death (stillborn 20 weeks gestation versus live birth). Results: The odds for denser breasts increased among women with PTD at <34 weeks gestation who were ≤45 years at time of mammogram (odds ratio (OR) and 95 confidence interval (CI)=2.8 (1.3–6.1)) and for whom <10 years had elapsed since pregnancy (OR=8.8 (1.7–45.8)). We observed similar increases in density among women with LBW (OR=3.3 (1.3–8.2)) when <10 years had elapsed. Conclusions: PTD and LBW may have a transitory effect on breast density.