Unilateral renal agenesis (one kidney)

In unilateral renal agenesis, one kidney does not develop while a baby is growing in the womb. (‘Unilateral’ means one side.) The other kidney usually looks and works as normal.

Most people have no long-term problems with unilateral renal agenesis, and some do not even know that they have only one kidney.

Unilateral renal agenesis: tests and diagnosis in pregnancy

The 20 week antenatal ultrasound scan looks at your baby growing in the womb. Unilateral renal agenesis may be suspected if one of the kidneys cannot be seen.

The scan also measures the amount of amniotic fluid (or liquor), the fluid that your baby floats in. The baby’s kidneys start making urine and pass this out into the amniotic fluid. This fluid protects your baby from getting hurt from the outside and helps his or her lungs mature so he or she is ready to breathe after birth.

If there is not enough amniotic fluid (oligohydramnios), this may mean that one or both kidneys are not working properly, and the baby may have problems breathing after birth.

What the ultrasound can tell us

Although your doctor will not always know how your baby will be affected at birth, he or she is less likely to have significant problems if: 

  • he or she is growing well in the womb
  • no other problems have been found, and
  • there is a normal amount of amniotic fluid. 

You may need to go back to the hospital for more ultrasound scans during the reainder of your pregnancy .


Your obstetrician may refer you to a paediatrician, a doctor who treats babies, children and young people, and may be in a hospital or clinic, or a paediatric nephrologist, a doctor who treats babies, children and young people with kidney problems, and may be in a hospital or clinic.

Antenatal hydronephrosis

Sometimes, unilateral renal agenesis can be seen with another condition that happens in the womb, called antenatal hydronephrosis. The other kidney does not drain urine properly. The affected kidney becomes stretched and swollen. Antenatal hydronephrosis often gets better at a later stage in the pregnancy, but your doctor will check how your baby is affected.

Unilateral renal agenesis diagnosis later in childhood

Sometimes, unilateral renal agenesis is only picked up after birth or when a child is older. It is usually found during a scan that a child is having for another reason, such as a urinary tract infection (UTI) or after an accident.

Tests after birth

After your baby is born, he or she may need some imaging tests (scans). These use special equipment to get images of the inside of the body. They are used to confirm that your child has only one kidney and look for any complications.

  • Ultrasound scan – looks at the shape and size of your baby’s kidneys and other parts of the urinary system. A small handheld device is moved around your child's skin and uses sound waves to create an image on a screen.
  • DMSA scan – a chemical that gives out a small amount of radiation is injected into one of your child’s blood vessels. This chemical is taken up by healthy parts of the kidney and a special camera takes pictures. This can check that the single kidney is normal.

Occasionally other imaging tests are needed.Your doctor will discuss this with you.

Complications and treatment

In most cases, babies do not need treatment. A small number of children have symptoms or complications, which may not happen until later in life. These may need follow up or treatment, such as medicines.

High blood pressure

People with only one kidney have a slightly higher risk of hypertension, blood pressure that is too high.

If your child has hypertension, he or she will need to reduce their blood pressure so it is in the healthy range. Your child will probably need to eat a no-added salt diet, and may need to take medicines, to control his or her blood pressure. It is also recommended that all children, especially those with hypertension, keep to a healthy body weight and exercise regularly.

Urinary tract infections

Some children get urinary tract infections (UTIs), when germs get into the urine and travel up the urinary tract (or system). Babies and children with UTIs may become irritable, have a fever, have pain on weeing, feel sick or be sick. 

If your child has a UTI, he or she will need to take antibiotics, medicines that kill the germs.

If you think your child has a UTI, seek medical advice.

Chronic kidney disease

In many people with unilateral renal agenesis the other kidney works normally. The normal kidney can work harder to compensate and do the work of two kidneys. 

Sometimes children with unilateral renal agenesis have an abnormality in the other kidney. This may include renal hypoplasia or renal dysplasia. Part or all of the kidney does not develop properly and is smaller than usual. The kidney can usually clean blood and make urine, but may not work as well as a kidney with no abnormality. 

If the other kidney does not work normally, your child may have reduced kidney function. He or she may be a greater risk of progressing to later stages of chronic kidney disease (CKD), and will need more monitoring.

About the future

Many children will not have long-term problems. The other kidney usually grows larger to help do the work of two kidneys. 

A small number may be at higher risk of problems later in life. 

Your child should be able to do all the things other children their age do . He or she can go  to nursery and school, play with other children and stay active. 

Follow up

In the first few years of his or her life, your child may need to go back to the hospital for some tests. Later, he or she will need to see your family doctor about once a year. It is important to go to these appointments, even if your child seems well. You will also have the opportunity to ask any questions. At these appointments your child may have:

  • his or her blood pressure measured, to check for hypertension
  • urine tests – to check for protein in his or her urine (proteinuria), which may be a sign of problems in the kidney. You  or a nurse will collect some of your child’s urine in a small, clean container. A dipstick is dipped into the urine – this is a strip with chemical pads that change colour if there is protein  in the urine . 

Living healthily 

Your child can help protect his or her kidney, and reduce the risk of hypertension later in life, by leading a healthy lifestyle through their child and adult years. This includes:

  • eating a healthy diet – with at least five servings of fruit and vegetables a day, taking care not to eat too much salt, sugar and fats (especially saturated fats)
  • getting plenty of exercise 
  • not smoking.

Further support

This can be a difficult and stressful experience for you and your family.

If you have any concerns or need additional support, speak with your doctor or nurse.

More information

  • Chronic kidney disease (CKD)

    A life-long condition in which the kidneys stop working as well as they should over time. A team of healthcare professionals will support your child.

  • Urinary tract infection (UTI)

    Urinary tract infections happen when germs get into the urine (wee) and travel into the urinary tract.

  • Blood pressure

    Blood pressure (BP) is the force, or pressure, that makes the blood flow round the body. It is very important that your child’s blood pressure is in a healthy range. If it is too high or too low, your doctor will try to find out what is causing this.