**2.1. Relevant embryology**

The urogenital system is represented by two major components: the urinary system and the genital system. Embryological and fetal kidneys, genital tract and the urinary system develop from intermediate mesoderm. The rhythm of growth and development of the collector tubes differs greatly during pregnancy. Until 15 weeks of gestation, the rhythm of development is very rapid and later decreases [1, 2].

The urinary tract is almost entirely developed from the intermediate mesoderm. The evolution implies different stages in development: pronephros, mesonephros and metanephros. These stages will appear successively in the craniocaudal direction and coexist over time. Intermediate mesoderm is divided in the upper cervical and thoracic region, resulting in nephrotomes [2, 3].

The mesonephric duct will give rise to the ureteral bud after the formation of the pronephros. This, after 15 generations of divisions, will lead to the formation of the ureter, the calves, the collector tubes and the kidney pelvis. The lack of formation or agenesis of the pronephros or of the mesonephric duct can lead to the total or partial absence of the kidney or to other anomalies of the reno-urinary tract [4, 5].

CAKUT (congenital anomalies of kidney and urinary tract) may be part of multi-organ processes in single-gene disorders, with dominant or recessive inheritance, as we can find in Fraser syndrome, the branchiootorenal syndrome, Kallmann syndrome, Ehlers-Danlos syndrome and others [5, 6].

The genitalia differentiation, which leads to female or male gender, starts at 7–8 weeks of pregnancy and finalizes at 12–13 weeks. Every fetus will develop female characteristics, because at the beginning of gestational period, the Mullerian and Wolffian structures coexist. If the Mullerian structure will suffer atrophy, due to testosterone and anti-Mullerian hormone effects, male sex structures will develop from the Wolffian structure, and the fetus will become a male. In the opposite circumstance, the fetus will become a female. In conclusion, from the embryological point of view, an individual could be a female if the masculine features will not develop [7, 8].
