How much do breasts grow during pregnancy?

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Believe it or not, this question is a pretty common one among moms-to-be. They want to know what to expect when they’re newly pregnant. Some may find their chests growing almost immediately and wonder when it’s going to stop, while others relish in their newly full bosom. Either way, most pregnant moms are curious as to how much breast growth they can expect to incur on their way to motherhood. That being said, the answer varies considerably.

Breast growth during pregnancy occurs as a result of hormonal influx. Estrogen and progesterone—two key sex hormones—begin to rise during early pregnancy. The estrogen boosts circulation and collagen, which thereby creates a fuller appearance to the breasts and also draws some visual attention to more prominent veins across the chest from increased blood flow. Also, progesterone is a primary culprit behind water retention—something most women will deal with at one point or another during pregnancy. Often, the initial growth women see in their breasts is nothing more than water weight.

As these hormones continue to increase during the first trimester, women’s breast size may go up more than a full cup size. This usually begins by around eight weeks alone. However, some women don’t experience any change in size at all at this stage. It may be fatty deposits, but most women do not gain much weight until the start of the second trimester. Where on their body someone gains weight matters, too. If a woman has always seen weight gains and losses reflected in her breast size even when not pregnant, she’s likely to gain and lose there during pregnancy, too.

Some of the added bulk in a woman’s chest that develops during pregnancy is also the growth of breast tissue and the expansion of milk ducts. Yes, the hormonal and physical processes of breastfeeding start very early on in pregnancy. Most of the increase in breast size during the second and third trimesters will be due to weight gain. By the end of 40 weeks, some women will see as increase of as much as two cup sizes.

After the birth of the placenta, a hormonal response is signaled to the body that it needs to start producing milk. As the production of estrogen and progesterone drop off, prolactin production kicks into overdrive. As a result, milk is produced. Most women will have their milk come in by day 5 after birth, but it’s perfectly normal to see it a few days earlier or later than that. The engorgement that comes with it will leave the breasts feeling even larger and fuller. If a woman doesn’t breastfeed, her milk will dry up and her hormones will level out. As a result, the breast size she gained during pregnancy will deplete. If she retains some of the weight she gained while pregnant, the new cup size may stick around longer. Those who breastfeed may see another increase in size as much as a cup size. When nursing a baby, breast tissue is stretched and actually lost in small amounts, so the overall size of the breasts may shrink after birth. Both the growth and loss of breast size can cause stretch marks and sagging skin. Wearing a supportive bra throughout pregnancy and the postpartum period and staying hydrated can help.

Cite this page: Danielle Bosley, "How much do breasts grow during pregnancy?," in, April 5, 2016, (accessed August 9, 2022).