Photo Credit: Getty Images
For many women the first hint that they are pregnant are the breast changes they experience. Women may notice an increase in size and possibly some tenderness very early, often before the pregnancy is confirmed.
During pregnancy the breasts will grow larger under the influence of hormones. This breast growth is a positive sign that the breasts are preparing for breastfeeding and something your lactation consultant may ask about when taking a breastfeeding history to confirm that breast development has occurred.
The hormone progesterone increases the size of the alveoli, the milk-producing units of the breast. The lobes, which are sections of the alveoli and connecting ducts, allow the milk to flow from the alveoli where the milk is made to the openings in the nipple. You can visualize the structure of the alveoli and the connecting ducts like bunches of grapes, except much smaller of course. The alveoli would be represented by the grapes, the ducts would be represented by the stems. The lobes would be one complete bunch of grapes with the top of the stem ending at the nipple.
The milk is made in the alveoli (grape) and travels down the ducts (stems) going from the smallest duct to the largest ending at a small pouch just under the areola, called the lactiferous sinus (which would be like a widening in the thickest part of the stem). The hormone estrogen promotes the growth and branching of this ductal system. Prolactin and other hormones also contribute to breast growth in pregnancy and preparation for breastfeeding.