The metanephroi begin to produce urine at 9 weeks of gestation, even as active nephrogenesis is ongoing. Such urination becomes essential for maintaining a normal volume of amniotic fluid. The placenta, however, is the organ responsible for removing waste products from the fetus.

The fetal kidney has a lobated surface appearance, which can be attributed to condensations of metanephric mesenchyme around the initial branches of the ureteric buds. This surface lobation, however, usually disappears around 4 or 5 years of age, as additional tissue fills in the sulcated areas. If fetal lobation persists into adulthood, it is an inconsequential anatomic variant; however, such lobations may be sometimes mistaken for cortical scarring.