Hydronephrosis is a condition where one or both kidneys become stretched and swollen as the result of a build-up of urine inside them.
It can affect people of any age and is sometimes spotted in unborn babies during routine pregnancy ultrasound scans. This is known as antenatal hydronephrosis.
Hydronephrosis does not generally cause any long-term problems if it's diagnosed and treated promptly.
Babies with the condition may not require any treatment at all.
But the condition can increase your chances of getting urinary tract infections (UTIs).
In severe cases that are left untreated, the kidneys may become scarred, which could lead to loss of kidney function (kidney failure).
Hydronephrosis is increasingly being found in unborn babies during routine ultrasound scans.
This is known as antenatal hydronephrosis. It's estimated to occur in at least 1 in every 100 pregnancies.
As a parent, it can be worrying to learn your baby has a problem with their kidneys.
But most cases of hydronephrosis in babies are not serious and should not affect the outcome of your pregnancy.
About 4 out of every 5 cases will resolve on their own before or within a few months of birth and will cause no long-term problems for you or your baby.
The remaining cases may require treatment with antibiotics to prevent kidney infections, and in some cases surgery may be needed.
Hydronephrosis does not always cause symptoms. If it does, these may develop quickly over a few hours or gradually over weeks or months.
Symptoms can include:
You should see your GP if you develop severe or persistent pain in your back or side, have symptoms of a UTI, or notice a change in how often you urinate.
They may refer you for an ultrasound scan to assess your kidneys.
Hydronephrosis in babies does not usually cause symptoms, but you should seek medical advice as soon as possible if your child develops signs of a possible UTI, such as a high fever without any other obvious cause.
Read more about diagnosing hydronephrosis.
Hydronephrosis diagnosed in pregnancy is usually mild. It's thought to be caused by an increase in the amount of urine your baby produces in the later stages of pregnancy.
In more severe cases, it may be caused by a blockage in the flow of urine from the kidneys to the bladder, backflow of urine from the bladder to the kidneys, or a blockage in the flow of urine out of the bladder.
In adults, hydronephrosis is commonly caused by:
Read more about the causes of hydronephrosis.
If you have hydronephrosis, your treatment will depend on what's causing the condition and how severe it is.
Pregnant women and babies with the condition may not require any treatment.
In adults, the first stage of treatment is often to drain the urine out of your kidneys by inserting a tube called a catheter into your bladder or kidneys.
This will help relieve the pressure on your kidneys.
Once the pressure has been relieved, the cause of the build-up of urine may need to be treated.
The treatments used will depend on why the condition developed.
Read more about how hydronephrosis is treated.