Pronephros is the earliest nephric developmental stage in humans, and comprises to the mature kidney structure of the most primitive vertebrates. It extends from the 4th to the 14th somite and consists of 6-10 tubule pairs. These spill into a pair of primary ducts that are formed at the same level, caudally extend, and eventually reach and spill into the cloaca. The pronephros is a vestigial structure that disappears completely by the 4th week of embryonic life in humans.
The pronephros forms early in development, at 22 days post-coitum (DPC) in humans.
In mice pronephros regresses around 10 DPC.