Reproductive determinants of mammographic density in black women.

Purpose: While high mammographic density has been established as one of the strongest, independent breast cancer risk factors, few studies have reported determinants of mammographic density in Black women. We aimed to identify reproductive-related characteristics associated with mammographic density in Black women.

Methods: In data from a large mammography repository established in the Black Women's Health Study, we used Cumulus software to assess mammographic density from digital screening mammograms in 5,905 women ages 40-74. We used linear regression models to quantify the associations of parity, age at first birth, age at last birth, history of breastfeeding, and duration of breastfeeding with percent mammographic density. Models were adjusted for age, body mass index, and other breast cancer risk factors.

Results: Among parous women age < 55 years, mean percent mammographic density was 2.0 percentage points (95% CI 0.3, 3.7) higher in women with a history of ≥ 3 births than in women with a history of only 1 birth. The magnitude of associations of number of births with mammographic density varied somewhat by age at first birth and age at mammography. We found no significant associations between other reproductive factors and mammographic density.

Conclusion: In this large population of Black women, a higher number of births was modestly associated with higher percent mammographic density. This association may in part be influenced by age at first birth and age at mammography.