Association of Parity and Infant Feeding Method with Breast Density on Mammography

Mammography (MMG) is widely used for the screening and diagnosis of breast cancer. High breast density on MMG prevents breast cancer detection. In the present study, we analyzed the effects of parity and infant feeding method on mammographic breast density.

Ninety women diagnosed as having breast cancer were analyzed. Using the results of medical questionnaires, subjects were grouped according to their parity and infant feeding method, into either nulliparity or parity, and formula-feeding or breastfeeding. Each group consisted of 30 consecutive women from 45 to 49 years. Nulliparous group was unaffected by either parity or breastfeeding, formula-feeding group was affected by parity but not breastfeeding, and breastfeeding group was affected by both parity and breastfeeding. Mammographic breast density was evaluated on the contralateral and cancer-free breast, and was classified into ≥ 50% dense as high breast density and < 50% dense according to the Boyd quantitative scale. The association of parity and infant feeding method with breast density on MMG was analyzed using the Fisher's exact test.

Regarding parity, high breast densities were observed in 40% and 17% of nulliparous and parous breasts, respectively. Nulliparous breasts had significantly higher density than parous breasts (p  =  0.010). Regarding infant feeding method, 17% of breasts in both the formula-feeding and breastfeeding groups had high densities. Infant feeding method was not associated with mammographic breast density (p  =  1.0).

Nulliparity is associated with higher breast density, and parity, regardless of infant feeding method, induces atrophic changes of breast tissue.