Renal agenesis is a condition in which one or both kidneys fail to develop before birth. The unilateral form, where one kidney is missing, affects roughly 1 in 1,000 live births. Bilateral renal agenesis, where both kidneys are absent, is far rarer at about 1 in 3,000 to 4,000 pregnancies, and carries a much more serious prognosis.
Unilateral vs. Bilateral Renal Agenesis
The distinction between having one missing kidney and having both missing changes everything about how the condition plays out. With unilateral renal agenesis, the remaining kidney typically compensates by growing larger and filtering blood at a higher capacity. Many people live full, healthy lives with a single kidney and may not even know they have the condition until an imaging scan reveals it for an unrelated reason.
Bilateral renal agenesis is a different situation entirely. Without any kidney function, a developing fetus cannot produce urine, which makes up most of the amniotic fluid in later pregnancy. The resulting lack of amniotic fluid (oligohydramnios) compresses the fetus and prevents the lungs from developing properly. This chain of events is known as Potter sequence.
What Causes It
Kidney development begins early in pregnancy when a small tube called the ureteric bud branches off from an existing duct and pushes into a cluster of cells called the metanephric mesenchyme. These two structures need to connect and exchange chemical signals for a kidney to form. If the ureteric bud fails to reach the mesenchyme, around day 11 of embryonic development in animal models, the cells that would have become kidney tissue die off. When this happens on one side, you get unilateral agenesis. When it happens on both sides, both kidneys fail to form.
Several gene mutations can disrupt this process. The RET gene, located on chromosome 10, is one of the most well-studied culprits and has been linked to both unilateral and bilateral forms. Other implicated genes include BMP4, FRAS1, FREM1, and UPK3A for unilateral cases, and FGF20 and ITGA8 for bilateral cases. These genes help regulate the signaling between the ureteric bud and the surrounding tissue. Beyond genetics, maternal diabetes and certain medication exposures during pregnancy can also increase the risk.
Potter Sequence and Bilateral Agenesis
Babies with bilateral renal agenesis develop a recognizable set of physical features collectively called Potter sequence. Because the fetus is compressed without adequate amniotic fluid, affected newborns often have a flattened nose, prominent skin folds near the eyes, low-set ears, and a recessed chin. Limb abnormalities are also common, including clubbed feet, hip dislocation, and shortened lower limbs.
The most life-threatening component is underdeveloped lungs. The degree of lung underdevelopment depends on how early amniotic fluid dropped and how long the fetus went without it. Newborns with severe pulmonary hypoplasia typically develop respiratory distress within an hour of birth. Historically, bilateral renal agenesis has been considered fatal shortly after delivery.
Associated Abnormalities
Renal agenesis rarely occurs in complete isolation. A review of 30 cases of congenital solitary kidney found that nearly half had additional urological tract abnormalities, about 30% had ear, nose, or throat anomalies, 27% had musculoskeletal problems, 23% had gastrointestinal issues, and 13% had cardiovascular differences. In males, unilateral agenesis is often associated with absence of the vas deferens on the same side. In females, it can occur alongside an underdeveloped uterine horn.
Several recognized genetic syndromes include renal agenesis as one component. The VACTERL association, for example, involves vertebral defects, anal abnormalities, cardiac malformations, tracheoesophageal problems, renal anomalies, and limb differences. Fraser syndrome combines renal anomalies with fused eyelids, genital differences, and webbed fingers. MURCS syndrome pairs absent kidneys with absent uterine structures and spinal abnormalities. When renal agenesis is detected, doctors often screen for these related conditions.
How It’s Diagnosed
Most cases are identified on prenatal ultrasound. The key finding is an empty renal fossa, the space where a kidney should be, without evidence of a kidney sitting in an abnormal location (ectopic kidney) or fused across the midline (horseshoe kidney). Doctors confirm the diagnosis by checking for renal arteries branching off the aorta. In unilateral agenesis, only one renal artery is visible. In bilateral agenesis, neither renal artery is present.
For bilateral agenesis, severely low amniotic fluid is often the first red flag, prompting a closer look at the kidneys. Unilateral agenesis is trickier because amniotic fluid levels stay normal and the remaining kidney may already be enlarged, appearing healthy on a routine scan. Some cases aren’t caught until childhood or adulthood, discovered incidentally during imaging for back pain, abdominal symptoms, or other unrelated complaints.
Living With One Kidney
For people with unilateral renal agenesis, the outlook is generally good, but it’s not entirely worry-free. The remaining kidney handles the full workload and usually adapts well, a process called compensatory hypertrophy. Over time, though, this extra demand carries some risks. There is an elevated chance of developing high blood pressure, protein in the urine (a sign of kidney stress), and gradual loss of kidney function.
The National Kidney Foundation recommends yearly monitoring that includes at least two tests: an eGFR blood test to measure how well the kidney is filtering, and a urine albumin-to-creatinine ratio to check for protein leaking into the urine. Keeping blood pressure well managed is one of the most important things you can do to protect a solitary kidney long-term. Staying hydrated, maintaining a healthy weight, and avoiding medications that are hard on the kidneys (like frequent use of certain over-the-counter painkillers) also help preserve function over decades.
Outlook for Bilateral Agenesis
Bilateral renal agenesis has historically been lethal because the lungs simply cannot support breathing after birth. In recent years, however, an experimental approach has shown some promise: serial amnioinfusions, where fluid is repeatedly injected into the uterus during pregnancy to give the lungs a chance to develop. A clinical trial published in JAMA found that 82% of live-born infants who received this treatment survived to at least 14 days and were able to have dialysis access placed. Longer-term survival was lower, and the infants faced significant health challenges beyond lung function, including the need for dialysis until a kidney transplant becomes possible.
This approach remains specialized and is not widely available. It represents a shift from a uniformly fatal diagnosis to one where survival is possible but comes with intensive, ongoing medical care from birth onward.