Blonde Girl With Big Breasts

The size of a woman's breasts may fluctuate during the menstrual cycle, particularly with premenstrual water retention. An increase in breast size is a common side effect of use of the combined oral contraceptive pill.
Breasts sag if the ligaments become elongated, a natural process that can occur over time and is also influenced by the breast bouncing while exercising (sports bra). Breasts can decrease in size at menopause if estrogen levels decline.