At approximately day 1

At birth, a rudimentary system of ducts has formed. Development at this stage is diverse, and can range from simple blunt-end tubular structures to well-developed, branching structures with acinar development.

Reference [PubMed Link]

Howard BA, Gusterson BA. 2000. Human breast development. Journal of Mammary Gland Biology and Neoplasia 5(2):119-137.

At approximately day 1

At birth, the ductal system opens onto the surface through the breast pit (a depression in the skin’s surface). The underlying mesenchyme proliferates to form an inverted nipple, and the skin surrounding the nipple proliferates to form the areola. Hair can be found at the periphery of the areola. Progesterone receptors first appear in the epithelium of the fetal breast between birth to 2-3 months of life.

Duration: 2 weeks

Reference [PubMed Link]

Howard BA, Gusterson BA. 2000. Human breast development. Journal of Mammary Gland Biology and Neoplasia 5(2):119-137.

At approximately day 1

Ovary weight is approximately 330 mg. Number of oogonia have been reduced to about 2 million at birth.

Reference [PubMed Link]

Rabinovici J, Jaffe RB. 1990. Development and regulation of growth and differentiated function in human and subhumand primate fetal gonads. Endocrine Reviews 11(4):532-557.

At approximately day 1

Oogenisis: Diplotene stage is completed shortly after birth (chromosomes separate and uncoil slightly, some DNA transcription can occur). Oocytes enter a suspended state and meiosis is arrested until puberty. Antral (Graafian) follicles, with a fully developed oocyte, fluid filled cavity (known as the antrum), multiple layers of granulosa cells, and a thecal layer (outside the basement membrane), can be found.

Duration: 2 weeks

Reference [PubMed Link]

Rabinovici J, Jaffe RB. 1990. Development and regulation of growth and differentiated function in human and subhumand primate fetal gonads. Endocrine Reviews 11(4):532-557.

At approximately day 1

At birth, the mammary gland has secretory activity (possibly due to maternal hormones) which subsides within 3-4 weeks after birth.

Reference [PubMed Link]

Russo J, Russo IH. 2004. Development of the human breast. Maturitas 49(1):2-15.