[Development of the upper urinary tract of the fetus during the 3rd trimester of pregnancy].

Increases in foetal renal size and weight were studied respectively in 232 and 160 different kidneys. All the organs are obtained from autopsy specimens, dead pre and full-term infants rigorously chosen; their ages ranging from 26 to 41 weeks of gestation. All the renal increases are in agreement with either the body length or the birth weight of the foetuses. With these data, the human kidney growth can be analysed quantitatively. This could be useful for the diagnosis by ultrasound in evaluating certain patients during the last three months. Confrontation of these values with the histological aspects shows different developmental stages. The kidney is a good index for gestational age assessment. The ureteral development was studied in 54 ureters from 27 foetuses with the same characteristics. Quantitative determinations by the point counting method of the different areas allows analysis of the myogenesis and of the evolution of the ureteral lumen area according to gestational age. Myogenesis is important up to around the 36th week, corresponding to nephrogenesis achievement. These modifications of the ureteral wall structure are accompanied by the slow and late connective tissue differenciation. They could explain the decrease of the luminal area during this foetal period and after birth.