Unilateral renal agenesis is a condition present from birth where one kidney does not develop. Many people with unilateral renal agenesis feel well and have no symptoms, so it may only be found during a routine scan or later testing for early signs of unilateral renal agenesis. It can be recognized before birth, in childhood, or in adulthood, and not everyone will have the same experience. Treatment often focuses on monitoring kidney health, blood pressure, and urine, and most people do well when the single kidney works normally. Life expectancy is often close to usual, but the outlook can vary if other urinary tract or birth differences are also present.
How many people live with Renal agenesis, unilateral?
Unilateral renal agenesis, meaning being born with one kidney instead of two, is not tracked by a single worldwide head count, but the commonly reported rate of about 1 in 1,000 to 1 in 2,000 births suggests roughly 4 to 8 million people worldwide may be living with it, with the range changing because some studies find more cases through prenatal scans than others (StatPearls, 2023; UN World Population Prospects, 2024). Using the same approach, about 170,000 to 340,000 people in the United States may be living with unilateral renal agenesis (StatPearls, 2023; U.S. Census Bureau, 2024).
Overview
Renal agenesis, unilateralSymptoms
Unilateral renal agenesis means one kidney never formed. Many people with unilateral renal agenesis have no obvious signs and feel well, often learning about it during a scan. Some may have urinary infections, high blood pressure, or lower kidney function.
Outlook and prognosis
Most people with unilateral renal agenesis do well and live a normal lifespan with one healthy kidney. For many, this means few or no day-to-day limits, though regular checkups help watch blood pressure, kidney function, and urine protein over time.
Causes and risk factors
Unilateral renal agenesis usually happens before birth when one kidney does not form. It can result from a new genetic change or run in families. Diabetes, certain medicines, and smoking during pregnancy may raise the risk in some cases.
Genetic influences
Genetics can be important in unilateral renal agenesis, but many cases happen without a clear inherited cause. Some are linked to gene changes or part of a broader syndrome, so genetic counseling may help, especially if there are other birth differences or a family history.
Diagnosis
Renal agenesis, unilateral is often suspected from clinical features or imaging findings, especially before birth or during scans done later for another reason. The diagnosis of renal agenesis, unilateral is usually confirmed with ultrasound and, if needed, genetic tests.
Treatment and drugs
Unilateral renal agenesis often needs no direct treatment if the single kidney works well. Care focuses on regular blood pressure, urine, and kidney function checks. Some people also need treatment for urinary tract problems and advice to protect the kidney.
Symptoms
Many people with unilateral renal agenesis feel completely well and only learn about it after an ultrasound or scan done for another reason. For many people with unilateral renal agenesis, the early features of unilateral renal agenesis are so mild that day-to-day life feels normal. When signs do appear, they usually relate to the single working kidney, nearby urinary tract differences, or higher blood pressure over time.
Many living with unilateral renal agenesis have no symptoms at all. The condition is often found by chance during pregnancy imaging, a routine checkup, or a scan for something else.
The single kidney often grows larger than usual because it is doing the work of two. This is usually seen on imaging and does not always cause any day-to-day problems.
Some people with unilateral renal agenesis also have differences in the urinary tract that make urine flow less smoothly. This can raise the chance of urinary tract infections, including burning with urination, fever, or side pain.
Over time, some people with one kidney develop high blood pressure. This may not cause noticeable symptoms at first, so regular blood pressure checks are important.
How people usually first notice Renal agenesis, unilateral?
Unilateral renal agenesis, meaning a person is born with only one kidney, is often not noticed at all at first because the single kidney usually grows larger and does the work of two. In many cases, the first signs of unilateral renal agenesis appear before birth on a routine prenatal ultrasound, when a doctor sees that one kidney is missing; in others, it is first found later by chance during imaging for abdominal pain, a urinary tract infection, or another unrelated reason. When it does cause early clues, families or doctors may notice problems linked to the urinary tract, high blood pressure, or, less often, differences in the genitals or other organs that can sometimes occur alongside this condition.
Types of Renal agenesis, unilateral
No distinct types of unilateral renal agenesis are widely recognized.
Can I slow down the onset of symptoms?
Usually no: unilateral renal agenesis means being born with only one kidney, so there is no proven way to delay the start of symptoms if they are going to happen, and many people never develop symptoms at all. What you can do is help protect the kidney you have; keeping blood pressure, blood sugar, and weight in a healthy range, not smoking, avoiding frequent use of pain relievers like ibuprofen or naproxen unless a clinician says they are safe, and staying well hydrated may lower the risk of later kidney strain, but this does not prevent the condition. Regular checkups to monitor blood pressure, urine, and kidney function are well established and can catch problems early, and while these steps cannot guarantee an outcome, they can help many people with one kidney stay well for years.
What genetics can tell you about symptoms
Genetics can sometimes help explain why some people with unilateral renal agenesis have only one missing kidney and no day-to-day symptoms, while others also have changes in the urinary tract, reproductive organs, or other parts of the body. In a small number of families, inherited gene changes are linked to this condition and may affect when related problems show up or how broad the pattern is, but they usually cannot predict exactly how severe symptoms will be. For many living with unilateral renal agenesis, the condition happens without a clear genetic cause, so genetic testing is most helpful when there are other birth differences, a family history, or concern about risks for relatives.
Causes and risk factors
For many families, the causes of unilateral renal agenesis are not fully clear because this kidney difference starts very early in pregnancy. Changes in genes that guide kidney and urinary tract growth can cause it, and these changes may be inherited or may happen for the first time in the baby. A family history of kidney or urinary tract birth differences can raise the chance of unilateral renal agenesis. Researchers are still learning how these pieces fit together. Risk factors for unilateral renal agenesis may also include diabetes or obesity in pregnancy, certain medicines, and some harmful exposures early in pregnancy, though most cases are not caused by anything a parent did.
What are the most common causes or risk factors?
In many babies born with one missing kidney, there is no clear cause; the kidney simply does not form as expected very early in pregnancy. The chance is higher if it runs in the family or happens as part of a genetic condition, although most cases are not inherited. Well-known non-genetic risk factors include diabetes before pregnancy and obesity in the birth parent.
Environmental and biological risk factors
Unilateral renal agenesis begins very early in pregnancy, often before anyone knows there is a problem. Many cases have no single clear cause, but doctors do know some risk factors for unilateral renal agenesis. Some risks are carried inside the body, others come from the world around us.
Unilateral renal agenesis can happen when the early tissue that should start one kidney, and the small tube that guides its growth, do not form or connect as they should. If that signal fails at a key moment, one kidney may never develop.
This condition is seen somewhat more often in males than in females. Sex does not cause the condition by itself, but it appears to influence how often it occurs.
Diabetes before pregnancy or high blood sugar early in pregnancy can raise the chance of kidney and urinary tract differences in the baby. This includes a higher risk of unilateral renal agenesis.
The kidneys, urinary tract, and some reproductive organs develop alongside one another very early in fetal life. When that shared developmental process is disrupted, unilateral renal agenesis is more likely.
Genetic risk factors
Many people with unilateral renal agenesis feel completely well and only learn about it during an ultrasound done for pregnancy care, belly pain, or another routine reason. When doctors look at the genetic risk factors for unilateral renal agenesis, they often focus on family history and genes that guide the kidney and urinary tract early in pregnancy. Carrying a genetic change doesn’t guarantee the condition will appear. Even so, many cases happen on their own, and no single genetic cause is found.
Family history: Having a parent, brother, sister, or child with one kidney or another urinary tract difference can raise the chance of unilateral renal agenesis. This pattern suggests that inherited gene changes may be involved, even when relatives have different symptoms.
Kidney development genes: Changes in genes that help build the kidneys and urinary tract before birth can lead to unilateral renal agenesis. Well-known examples include PAX2, HNF1B, EYA1, RET, and GREB1L, although testing does not find a cause in every family.
New gene changes: Sometimes the genetic change starts for the first time in the baby and is not found in either parent. This can explain why unilateral renal agenesis may appear in a family with no earlier history of kidney differences.
Genetic syndromes: In some people, unilateral renal agenesis is one feature of a broader inherited condition rather than an isolated finding. This is more likely when the single kidney occurs along with hearing loss, eye differences, genital or reproductive tract differences, or other birth differences.
Chromosome changes: A small missing or extra piece of a chromosome can sometimes disrupt genes needed for kidney formation. These chromosome changes are less common, but they are a recognized genetic cause, especially when there are several birth differences together.
Dominant inheritance: In some families, a change in just one copy of a gene is enough to increase risk. One relative may have a single kidney while another has a milder urinary tract finding or no obvious signs at all.
Lifestyle risk factors
With unilateral renal agenesis, one kidney is present from birth, so lifestyle habits do not cause the condition. However, how lifestyle affects unilateral renal agenesis matters because the single working kidney can be placed under extra strain over time. The main concerns are preserving kidney function, controlling blood pressure, and lowering the chance of injury or added kidney damage.
Eating a very salty diet can raise blood pressure, which increases stress on a single kidney. Keeping sodium intake moderate may help protect long-term kidney function.
Overweight and obesity can increase the risk of high blood pressure, diabetes, and kidney overwork. Maintaining a healthy weight may reduce the chance of complications in people with unilateral renal agenesis.
Too little physical activity can make weight gain, poor blood pressure control, and insulin resistance more likely. Regular exercise can support heart and kidney health when it is matched to the person's overall condition.
Repeated dehydration can reduce kidney perfusion and may increase the risk of kidney stones or urinary problems. Steady fluid intake is often an important part of how lifestyle affects unilateral renal agenesis, especially during heat or exercise.
Risk prevention
Unilateral renal agenesis means being born with one kidney instead of two. In most cases, the condition itself cannot truly be prevented, because it develops early in pregnancy and may happen without a clear cause. Prevention for people with unilateral renal agenesis is mostly about protecting the single working kidney and lowering the risk of future kidney damage. Prevention works best when combined with regular check-ups.
Some cases of unilateral renal agenesis cannot be avoided, but good prenatal care may lower certain pregnancy-related risks. Avoiding alcohol, smoking, and nonessential medicines in pregnancy can help support normal fetal development.
Managing diabetes and high blood pressure before and during pregnancy may reduce the chance of some birth differences. This is especially important when there is a family history of kidney or urinary tract problems.
Many living with unilateral renal agenesis do well, but regular urine, blood pressure, and kidney function checks help catch strain early. This can matter even when there are no clear early symptoms of unilateral renal agenesis later in life.
Protecting the single kidney is a key part of prevention. Ask a doctor about sports safety, seat belt fit, and whether protective gear is sensible for higher-impact activities.
Can you prevent Renal agenesis, unilateral?
Usually, no. Unilateral renal agenesis, which means being born with one kidney instead of two, happens very early in pregnancy and often has no clear cause, so it usually cannot be prevented. Good prenatal care and avoiding things that can harm a developing baby, such as smoking, alcohol, and some medicines, may help lower risk in some pregnancies, but they cannot guarantee prevention.
Transmission
Unilateral renal agenesis is not infectious, so it cannot be caught from someone else through contact, the air, food, or sex. It develops before birth, when one kidney does not form.
When people ask about how unilateral renal agenesis is inherited, the answer is that many cases happen sporadically, with no clear family history. Sometimes, though, unilateral renal agenesis is linked to a genetic change that can run in families and be passed from a parent to a child, so the chance of it happening again may be higher in some families. If there are other kidney or urinary tract differences in close relatives, a genetics specialist can help explain the genetic transmission of unilateral renal agenesis and what it may mean for future pregnancies.
When to test your genes
Consider genetic testing if unilateral renal agenesis is found before birth or in childhood and there are other urinary tract differences, hearing loss, genital anomalies, or a family history of kidney malformations. Testing can clarify syndromic causes and guide kidney monitoring and family planning.
Diagnosis
Unilateral renal agenesis is often found before birth on a routine ultrasound or later when imaging is done for another reason. Many people living with this condition have no symptoms, so the diagnosis of unilateral renal agenesis may come as a surprise. Doctors usually confirm it by showing that one kidney is missing and checking that the other kidney is present and working well.
A pregnancy ultrasound may show that one kidney cannot be seen while the other appears larger than usual. Doctors also look at the bladder and the amount of amniotic fluid to help judge how well the urinary system is developing.
After birth, a kidney ultrasound is usually the first test to confirm that only one kidney is present. It also helps check the size and shape of the working kidney and look for swelling or other urinary tract changes.
If the ultrasound is not fully clear, your provider may suggest MRI or a CT scan to look closer. These scans can help confirm that the kidney is truly absent rather than hidden by an unusual position.
Blood and urine tests are often done to see how well the single kidney is working. They may also check for protein in the urine or other early signs of kidney strain.
How is Renal agenesis, unilateral diagnosed?
Unilateral renal agenesis, which means one kidney did not form, is usually diagnosed with imaging tests that show only one kidney, most often an ultrasound before birth or later in childhood or adulthood. If the picture is not clear, doctors may use other scans such as a CT scan or MRI, and they often do blood and urine tests to check how well the single kidney is working and to look for related differences in the urinary tract. Genetic testing is not needed for everyone, but it may be offered if there are other birth differences, a family history, or signs that it could be part of a wider genetic condition.
Stages of Renal agenesis, unilateral
Renal agenesis, unilateral does not have defined progression stages. This is because it is a difference present from birth, where one kidney never develops, rather than an illness that usually moves step by step over time. Doctors usually start with a conversation about how unilateral renal agenesis is diagnosed, then confirm it with imaging such as a prenatal ultrasound, an ultrasound after birth, or sometimes a CT or MRI scan done for another reason. Follow-up often includes blood pressure checks, urine testing, and kidney function blood tests to make sure the single working kidney stays healthy.
Outlook and prognosis
The outlook for unilateral renal agenesis is usually very good, and many people live a normal lifespan with one healthy kidney and few or no symptoms. Prognosis depends mainly on how well the remaining kidney functions and whether there are associated urinary tract, genital, or other congenital abnormalities. Some individuals have an increased lifetime risk of hypertension, proteinuria, or reduced kidney function, so periodic follow-up with blood pressure checks, urinalysis, and kidney function testing is often recommended. Mortality is generally not increased when unilateral renal agenesis occurs in isolation and the solitary kidney remains healthy. Outcomes can be less favorable if there is reflux, obstruction, dysplasia of the remaining kidney, or syndromic involvement. In practice, the long-term prognosis of unilateral renal agenesis is excellent for most patients, especially when the condition is recognized early and monitored appropriately.
Long-term effects
Many people with unilateral renal agenesis live full lives and may not notice day-to-day problems for years. The long-term picture is often shaped by how well the single kidney grows and keeps up with the body’s needs over time. Long-term effects vary widely, and some people have few health issues while others develop kidney-related problems later in childhood or adulthood. Thinking about the long-term effects of unilateral renal agenesis helps explain why doctors follow kidney function over many years.
One kidney can often do the work of two, but over time that extra workload may put stress on the filtering units. In some people, this can gradually lower kidney function, especially later in life.
People with unilateral renal agenesis have a higher chance of developing high blood pressure as they get older. This may be one of the earliest signs that the single kidney is under strain.
The kidney may start leaking small amounts of protein into the urine, which can be an early marker of kidney stress. This change may appear before there is a clear drop in kidney function.
Some people develop chronic kidney disease over time, meaning the kidney does not filter blood as well as it should. The risk is not the same for everyone and is higher when other urinary tract differences are also present.
How is it to live with Renal agenesis, unilateral?
Many people living with unilateral renal agenesis, meaning they were born with only one kidney, feel completely well and go through daily life much like anyone else, often without symptoms at all. The main practical implication is protecting that single kidney over a lifetime, which can mean regular checkups, attention to blood pressure, staying well hydrated, and being cautious with kidney-straining medicines or high-impact activities if a clinician advises it. For family members and other close people, the condition usually does not create major day-to-day limitations, but it can bring some understandable worry and a shared focus on healthy habits and follow-up care.
Treatment and drugs
Many people with unilateral renal agenesis live normal lives with one working kidney and do not need specific medicine for the missing kidney itself. Treatment for unilateral renal agenesis usually focuses on protecting the remaining kidney with regular checkups, blood pressure control, urine and blood tests, and advice to avoid kidney strain, such as staying well hydrated and being careful with frequent use of pain relievers like ibuprofen or naproxen. Alongside medical treatment, lifestyle choices play a role. If unilateral renal agenesis is linked to urine flow problems, repeated urinary tract infections, or other urinary tract differences, treatment may include antibiotics, surgery, or care from a kidney or urinary specialist, while kidney failure treatment such as dialysis or transplant is only needed if the single kidney becomes severely damaged, which is uncommon.
Can you cure Renal agenesis, unilateral?
No, there is no cure for unilateral renal agenesis, which means being born with only one kidney. The missing kidney cannot be grown back, but many people with this condition live healthy lives if the other kidney works well. Care usually focuses on protecting that kidney with regular checkups and treating any problems, such as high blood pressure or infections, if they come up.
Non-drug treatment
Living with one working kidney often does not change daily life much, but it does mean that protecting kidney health matters over time. In unilateral renal agenesis, there is no non-drug treatment that can replace the missing kidney, so care focuses on monitoring, healthy habits, and preventing strain on the kidney you have. Many people with unilateral renal agenesis feel well for years and only need regular checkups, especially if there are no early symptoms of unilateral renal agenesis. Managing this condition often centers on simple steps that help lower the chance of high blood pressure, protein in the urine, or reduced kidney function later on.
Ongoing follow-up is a main part of care for unilateral renal agenesis. Blood pressure checks, urine tests, and kidney function monitoring can help catch changes early, even when you feel well.
Imaging may be used to confirm the diagnosis and watch how the working kidney grows and adapts. In children, this can help doctors look for related urinary tract differences that sometimes occur alongside unilateral renal agenesis.
Drinking enough fluid helps support normal kidney function, especially during hot weather, exercise, or illness with vomiting or diarrhea. Your care team can advise what is right for your age and health, since more is not always better.
A heart-healthy eating pattern with sensible salt intake can help protect blood pressure and kidney health over time. If kidney function stays normal, most people do not need a highly restrictive diet.
Your genes may have an impact on how drugs work for you
For people with unilateral renal agenesis, genetic testing is not usually used to pick everyday medicines, because there are no well-established gene-based drug rules that are specific to this condition. What usually matters more is that you are living with one kidney, so some medicines that the kidneys clear from the body may build up more easily or put extra strain on the kidney, which can mean lower doses, closer blood and urine checks, or avoiding certain pain relievers and other kidney-stressing drugs. If the missing kidney is part of a broader inherited condition, your care team may look at that bigger picture too, but medicine choices are still most often guided by how well the kidney is working rather than by a specific gene result.
Pharmacological treatments
Most people with unilateral renal agenesis do not need medicine just for having one kidney. Drug treatment is used when related problems show up, such as high blood pressure, urine infections, or signs that the single kidney is under strain. In children and adults, treatment depends on kidney function, urine findings, and whether there are urinary tract problems. If you are wondering about treatment for unilateral renal agenesis, the answer is often careful monitoring first, with medicines added only if needed.
There is no standard medicine that can make a missing kidney grow back or directly treat unilateral renal agenesis. Many living with this condition take no daily prescription at all if the remaining kidney is working well.
Antibiotics are used if a urinary tract infection develops, which can matter more when there is only one working kidney. The exact drug depends on age, symptoms, and the bacteria causing the infection.
Medicines such as lisinopril, enalapril, losartan, or valsartan may be used if high blood pressure or protein in the urine is present. These drugs can help protect the single kidney over time as well as lower blood pressure.
Water pills such as hydrochlorothiazide or furosemide may be added when blood pressure is not controlled or the body is holding extra fluid. Dosing may be increased or lowered gradually to match kidney function and response.
Genetic influences
Many people living with unilateral renal agenesis do not have a clear inherited cause, and the missing kidney seems to happen by chance while the urinary system is forming before birth. In others, genetics do play a role, and a change in a gene involved in early kidney development can raise the chance of unilateral renal agenesis, sometimes along with other differences in the urinary tract or nearby body systems. Family history is one of the strongest clues to a genetic influence. The effect can vary a lot within the same family, so one relative may have a single kidney while another has milder urinary tract changes or no obvious symptoms at all. When there is a family history of unilateral renal agenesis, or when it appears with other birth differences, doctors may suggest genetic counseling and sometimes testing to help clarify the cause and what it could mean for other family members.
Is Renal agenesis, unilateral genetic?
Genetics can be important in unilateral renal agenesis, but many cases happen without a clear inherited cause. Some are linked to gene changes or part of a broader syndrome, so genetic counseling may help, especially if there are other birth differences or a family history.
Having a genetic risk is not necessarily a diagnosis
Across the general population, genetic variants are common and are a normal part of human biology. Most do not directly affect health and are simply part of natural human diversity. For many genes, having a variant linked to a condition suggests a possible association, not a definite diagnosis, especially when several genes and environmental factors are involved. In some cases, though, one well-understood variant in a particular gene can be enough to confirm a diagnosis.
Pharmacogenetics—how genetics influence drug effects
For many living with unilateral renal agenesis, treatment is less about fixing the missing kidney and more about protecting the kidney that developed. Genes involved in kidney development can sometimes help explain why one kidney did not form and whether doctors should also check for related differences in the urinary tract or, in some people, the reproductive organs. Genetics is only one factor, but when unilateral renal agenesis is part of a broader inherited condition, care may include closer follow-up and a conversation about family risk.
There is no proven gene-based drug treatment that is routinely used specifically for isolated unilateral renal agenesis. Instead, medicines are chosen mainly based on how well the single kidney is working and whether problems such as high blood pressure or protein in the urine have appeared. This is why treatment for unilateral renal agenesis often includes careful review of pain relievers like ibuprofen, some antibiotics, and contrast dye used in scans, since these may need caution or dose changes to help keep the remaining kidney healthy.
Interactions with other conditions
Many people with unilateral renal agenesis live day to day without major symptoms, but other health issues can matter more because they have only one working kidney. If that kidney is affected by high blood pressure, diabetes, repeated urinary tract infections, kidney stones, or a blockage in the urinary tract, kidney function may drop faster than it would in someone with two kidneys. Doctors call it a “comorbidity” when two conditions occur together, and in this setting those added problems can shape long-term kidney health. Some living with unilateral renal agenesis also have differences in the urinary tract, genitals, or reproductive organs, which can raise the chance of infections, trouble with urine flow, or fertility-related concerns. For many, this can mean that early symptoms of kidney problems, such as swelling, tiredness, foamy urine, or rising blood pressure, deserve prompt medical attention. With regular checkups and protection of the remaining kidney, many people with unilateral renal agenesis do well even if another condition is present.
How genes can cause diseases
Humans have more than 20,000 genes, each carrying out one or a few specific functions in the body. One gene instructs the body to digest lactose from milk, another tells the body how to build strong bones and another prevents the body's cells from beginning to multiply uncontrollably and developing into cancer. As all of these genes combined are the building instructions for our body, a defect in one of these genes can have severe health consequences.
Through decades of genetic research, we know the genetic code of any healthy/functional human gene. We have also identified that in certain positions on a gene, some individuals may have a different genetic letter from the one you have. We call these hotspots "Genetic Variations" or "Variants" in short. In many cases, studies have been able to show that having the genetic letter "G" in the position makes you healthy, but having the letter "A" in the same position disrupts the gene function and causes a disease. Genopedia allows you to view these variants in genes and summarizes all that we know from scientific research, which genetic letters (Genotype) have good or bad consequences on your health or on your traits.
What other conditions can cause similar symptoms to Renal agenesis, unilateral?
If one kidney seems to be missing, or if someone has repeat urine infections, side pain, or high blood pressure, doctors also think about a kidney that is there but sitting in the wrong place, a kidney that did not develop normally and does not work, or a kidney that became very small after damage or long-term blockage. Other urinary tract problems, such as urine flowing backward toward the kidney or a blockage where urine drains out, can cause similar problems too. Imaging tests are usually what help tell these apart from being born with only one kidney.
History
For many people, unilateral renal agenesis comes to light almost by accident. Someone may have an ultrasound for belly pain, a sports injury, or a pregnancy checkup and learn that they were born with only one kidney. In others, it may be found earlier, before birth or in infancy, especially if there are other urinary tract differences.
Across cultures and time periods, families and doctors likely noticed that some babies were born with differences in the urinary system, but older medicine could only describe what could be seen at birth or found during surgery or autopsy. Because imaging did not exist, unilateral renal agenesis was often missed in people who felt well and whose single kidney worked normally. That meant early medical reports tended to focus on more severe cases or on babies who had other birth differences as well.
As medical science evolved, the history of unilateral renal agenesis changed with the arrival of better imaging. X-rays, intravenous dye studies, ultrasound, CT scans, and MRI made it much easier to see whether one kidney had developed and whether the remaining kidney was larger from doing extra work. These tools also helped doctors understand that many living with unilateral renal agenesis can stay healthy for years, while some have related issues such as urine flow problems, high blood pressure, or changes in kidney function over time.
Prenatal ultrasound was another major step. It allowed unilateral renal agenesis to be recognized before birth in many pregnancies, which gave families and care teams more time to look for other differences in the kidneys, urinary tract, or nearby organs. This also improved follow-up after delivery, since some children with early symptoms of unilateral renal agenesis need monitoring even if they seem well at first.
Researchers later identified a genetic cause in some families and found that kidney development in the womb can be affected by several biological pathways, although not every case has a clear explanation. Over time, this shifted thinking away from viewing unilateral renal agenesis as a single, isolated finding in every person. Today, it is understood as a developmental difference that can range from an incidental finding to part of a broader pattern of birth differences, and that history helps explain why evaluation and follow-up are often tailored to the individual.