Fetal genital development

Fetal genital development refers to the sequence of events which leads to the development of the genitals and their adnexa.

Sequence
A few weeks after fertilization, the initial appearance of the human fetal genitalia is basically feminine: a pair of "urogenital folds" with a small protuberance in the middle, and the urethra behind the protuberance.

In typical fetal development, the presence of the SRY gene causes the fetal gonads to become testes; the absence of it allows the gonads to continue to develop into ovaries. Thereafter, the development of the internal reproductive organs and the external genitalia is determined by hormones produced by fetal gonads (ovaries or testes) and the cells' response to them.

If the fetus has testes, and if the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings swell, wrap around the penis, and fuse in the midline to form the penile urethra.

If testosterone is not present, normal female development continues, with the development of a perineal urethra and the formation of a uterus, clitoris and vagina.

The Müllerian ducts, which are paired ducts of the embryo which empty into the cloaca, and which develop into the upper vagina, cervix, uterus and oviducts; in the male they disappear except for the vestigial vagina masculina and the appendix testis.

Although female development is usually considered the "default" configuration in the absence of induction, recent evidence has indicated that Wnt4 plays a role in the development of female anatomy.

Homologies
Because of their common origin in fetal anatomy, a number of male and female anatomical features are said to be homologous; for example, the clitoris and penis are homologous with one another, as are Skene's glands in females and the prostate gland in males.

Intersexuality
Most of the time, the result of fetal genital development follows the stereotypical male or stereotypical female development path. However, in a small but significant minority of cases, the path of development follows an intermediate or other pathway, leading to what are called "ambiguous genitalia", one condition of those known as intersexuality.

See congenital anomalies of the genitalia for a list of congenital disorders caused by problems with fetal genital development.