Hydronephrosis is a condition in which the kidneys are swollen from a build-up of urine. In this handout, you will learn about hydronephrosis and how we treat it. You will also learn about the long-term outlook for your baby.

What is Hydronephrosis?

Hydronephrosis is a condition in which the kidneys are swollen from a build-up of urine. The build-up is caused by a blockage (something blocking the urine from flowing out) in the kidney pelvis (where the kidney connects to the ureter, or tubes that let urine flow out). It can also be caused by urine flowing in the opposite direction as it leaves the bladder. The kidneys help filter waste products in the body and make urine.

Hydronephrosis is a common condition. About one out of every 100 babies is born with hydronephrosis. It usually affects boys more than girls. Hydronephrosis can be range from mild to severe. Almost all types of hydronephrosis can be treated. Doctors can also watch your child’s kidneys over time to make sure they are as healthy as possible.

What Causes Hydronephrosis?

Hydronephrosis is caused by a blockage in the ureter. The blockage does not let urine flow through, so the urine builds up and the kidneys swell. You might hear us call these blockages ureteropelvic junction obstructions or ureterovesical juction obstructions. Both of these mean there is a blockage at the narrow point where the ureter (urine tube) meets the kidney or bladder.

Baby with diagram of kidneys and bladder.
This picture shows where your baby's kidneys, ureters and bladder are located. Image courtesy of Piktochart®


How Do Doctors Diagnose Hydronephrosis?

We diagnose hydronephrosis through an ultrasound of your baby’s kidneys at 12-20 weeks of pregnancy.

We also do follow-up ultrasounds at 34-37 weeks and one week after birth to check how much hydronephrosis has affected your baby’s kidneys. If your baby has hydronephrosis, you will meet with one of our pediatric urologists (doctor who cares for problems with the urinary tract). He will talk with you about treatment and follow-up care.

How Do Doctors Treat Hydronephrosis?

In many cases, mild or moderate hydronephrosis goes away on its own after birth. For babies with severe hydronephrosis, it usually gets better a few months after surgery.

What is the Long-Term Outlook For My Baby?

Your baby will likely live a healthy, normal life if the hydronephrosis goes away on its own or is treated with surgery.

If your baby has surgery, he will have regular follow-up care with a pediatric urologist.