During lactation, the mammary glands become enlarged by the action of estrogen and lactogen, and the lobules of the mammary glands become significantly enlarged, with milk-filled lobules resembling round bumps palpable on deep palpation. This is a sign of milk accumulation, which will affect the flow of milk and needs to be massaged to dissipate. Lastly, breast fibroids, which are small and undetected before pregnancy, increase rapidly during pregnancy and lactation and can be palpated as a lump like a round pimple, which can be surgically removed after breastfeeding.