Fetal hydronephrosis of 23mm is considered severe hydronephrosis and may not recover after birth.
Generally, it will be graded according to the level of fetal hydronephrosis, normal is 0-4mm, mild hydronephrosis is 5-9mm, moderate hydronephrosis is 10-15mm, and severe hydronephrosis is more than 15mm.
Mild to moderate hydronephrosis usually recovers after birth because the area of hydronephrosis is relatively small while not compressing the renal cortex. As the environment changes after birth and the fetus begins to urinate, most of it will gradually decrease or even disappear.
However, at present, the fetal hydronephrosis has reached 23mm, which can be judged as severe hydronephrosis, and should belong to pathological hydronephrosis. At this time, fetal kidney function has been impaired, so it is usually not possible to recover after birth, even after timely treatment. There may be no way to restore the renal function completely.