Conditions + Treatments

Hydronephrosis in Children

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What is hydronephrosis?

Hydronephrosis is a condition, affecting about 1 in 100 babies, where urine overfills or backs up into the kidney, causing the kidney to swell. Infants with hydronephrosis may be diagnosed before (prenatal) or after (postnatal) birth. 

In many of the children who are diagnosed prenatally, the condition disappears spontaneously by the time of birth or soon after. In children who have mild or sometimes moderate hydronephrosis, kidney function is commonly unaffected and the condition may resolve over a period of time after delivery.

Hydronephrosis affects the drainage of urine from the urinary system — the kidneys, ureters, bladder and urethra. When the urinary system is impaired, this can cause the urine to back up and the kidney to swell. Typically, hydronephrosis is caused by either something blocking urine flow or by urine leaking backward through the urinary system (reflux).

Your doctor will describe your child’s hydronephrosis as mild, moderate or severe — based on how much the kidney is stretched and how much the urinary flow is impaired — and will tell you whether your child’s hydronephrosis affects one kidney (unilateral) or both kidneys (bilateral). More than half of the cases resolve by the time the baby is born or soon after.

Care for hydronephrosis

At Boston Children’s Hospital, we are here to help. Our physicians and nurses are trained in pediatric urology and have extensive experience with hydronephrosis. We are ranked #1 in the nation and have the largest pediatric urology service in the world.

Learn more about how Boston Children's treats prenatal and postnatal hydronephrosis.


We are grateful to have been ranked #1 on U.S. News & World Report's list of the best children's hospitals in the nation for the third year in a row, an honor we could not have achieved without the patients and families who inspire us to do our very best for them. Thanks to you, Boston Children's is a place where we can write the greatest children's stories ever told.”
- Sandra L. Fenwick, President and CEO

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