Hormonal changes occur with estrogen production.
Mammary ducts begin to grow, fat increases and fibrous tissue becomes more elastic.
Once ovulation begins, the hormone progesterone will help the breasts to fully develop. Some areas of the breasts are affected worse than other areas and some women are affected worse than other women. This is why women should schedule a mammogram 7-10 days after the first day of their menstrual cycle. This is also the best time to perform a breast self-examination. Acini develop within the lobules to produce milk.