Many people have never heard of the term hydronephrosis. That’s because it is only prevalent in around 1% of the general population according to a research paper published by Science Direct. Hydronephrosis can affect both children and adults. In fact, it can even affect babies in the womb; this can be found via prenatal ultrasound. The same study by Science Direct observed that 1 in 100 to 200 fetuses suffered from hydronephrosis.