At approximately day 1

Vagina begins to develop.

Reference

O’Rahilly R, Muller F. 2001. Human embryology & teratology. Third edition. New York: Wiley-Liss.

At approximately day 1

Mammary buds lengthen, branch and begin canalize to form lactiferous ducts.

Reference [PubMed Link]

Pryor JL, Hughes C, Foster W, Hales BF, Robaire B. 2000. Critical windows of exposure for children’s health: the reproductive system in animals and humans. Environ Health Perspect 108 (Suppl 3):491-503.

At approximately day 1

Germ cells are now termed “primary oocytes.”

Duration: 30 weeks

Reference [PubMed Link]

Picton HM. 2001. Activation of follicle development: the primordial follicle. Theriogenology 55(6):1193-1210.

At approximately day 1

Oogenisis: Leptotene stage (chromosome condensation) of meiois begins, maximum number of oocytes in this stage occurs at 14-26 weeks.

Duration: 16 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

Oogenesis: Preleptotene stage (prochromosome condensation) of meiosis is reached by a majority of the fetal oocytes. Maximum number of oocytes in this stage is at 11-13 weeks.

Duration: 23 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.