Breasts begin to develop in the womb along the mammary ridge.
Although breasts begin to develop in utero, or in the womb, their growth and changes continue over the entire lifetime. Humans are the only mammal known for growing full breasts prior to needing to nurse. Milk glands begin to develop during puberty, and after approximately age 35 decrease in number in a process called involution.
Breasts in Infancy
In female infants, the chest area begins to thicken in the womb. This area is called the mammary ridge or milk line. At birth, the beginning of the milk duct system has already formed, and nipples are present. At this point, prior to puberty, only the nipple is raised.
Beginning Growth
The lobes of the breast develop first. Mammary glands are second to develop, and these glands are made of 15 to 24 separate lobes. At the onset of puberty, when the ovaries begin to secrete estrogen, fat tissue within the breast expand and cause the breast to fill out and grow. Milk ducts also begin to grow at this time.
Puberty
At the onset of menstrual periods, the breasts produce secreting glands at the ends of the milk ducts, and become mature. Breast growth varies between women in terms of the time it takes for the milk duct system to fully develop and grow. The breasts will reach full size between three and five years from the onset of development.
Developed Breasts
Fluctuating hormone levels during the menstrual cycle cause the breasts to change in size. Glands in the breast prepare for a potential pregnancy, and may also change in texture during the menstrual cycle. The breasts will return to normal size if a pregnancy is not achieved.
Expansion in Pregnancy
According to Ohio State University Medical Center, many physicians believe the breasts are not fully mature until a woman has given birth and produced milk. One of the earliest changes in pregnancy is within the breasts, which happens due to increased progesterone levels. After the breasts increase in size, the areolas grow as well. Tenderness may be present very early in pregnancy due to hormonal changes and expansion of breast tissue.
Increasing Breast Growth
Breast shape and size is mostly hereditary. Many creams and exercises are purported to increase breast size, but the only way to truly increase the size of the breasts is through a surgical augmentation. Breasts may grow during pregnancy, but for the most part return to their pre-pregnancy size after birth and/or nursing.
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