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Mammography and the Menstrual Cycle

One hypothesis proposed to explain why mammography is not as effective for women aged 40-49 years as it is for women aged 50 years and older is that a higher proportion of younger women have dense breast tissue, and increased breast density decreases the detection of cancer. To investigate whether breast density varies according to time in a woman's menstrual cycle, White et al. (p. 906) studied 2591 premenopausal women aged 40–49 years who had a screening mammogram and were not taking hormone supplements. The authors found evidence that the frequency of extremely dense, and therefore harder to read, mammograms for premenopausal women in their forties is lower when the mammogram is taken during the first and second week (follicular phase) of the menstrual cycle instead of during the third and fourth week (luteal phase).

“If these results are confirmed by future studies, timing of a woman's mammogram during the follicular phase of her menstrual cycle may improve the accuracy of mammography for women in their forties.”