What are dense breasts and how do they affect my mammogram?

Dense breasts have more glandular and connective tissue than fatty tissue. Breast density is divided into four categories (A, B, C and D) that range from almost entirely fatty to extremely dense. Federal regulations require that patients be told if they have dense breasts – categories C and D are considered dense.

• Categories A and B are not dense.
• Categories C and D are dense.

About half of women over 40 have dense breasts. Breast density changes over a woman's lifetime and can only be identified through an annual mammogram.