Renal agenesis is a condition in which a newborn is missing one or both kidneys. Unilateral renal agenesis (URA) is the absence of one kidney. Bilateral renal agenesis (BRA) is the absence of both kidneys.
Both types of renal agenesis occur in fewer than 1 percent of births annually, according to the March of Dimes. Fewer than 1 in every 1,000 newborns has URA. BRA is much rarer, occurring in about 1 in every 3,000 births.