Skip Ribbon Commands
Skip to main content
Health Issues

Prenatal Hydronephrosis (Urinary Tract Dilation)

By: Darcy Weidemann, MD FAAP & Juan C. Kupferman, MD, MPH, FAAP

Hydronephrosis, also called urinary tract dilation, happens when urine backs up into the kidney. This causes swelling in the kidney's drainage system. When the hydronephrosis is found during pregnancy, it is called prenatal hydronephrosis.

Prenatal hydronephrosis is relatively common, affecting about 1 in 100 babies. In fact, it is the most common problem found on a prenatal ultrasound.

Hydronephrosis can affect just one kidney (called unilateral) or both kidneys (called bilateral). Prenatal hydronephrosis is graded on a scale that ranges from mild to moderate to severe. It depends on how much swelling there is in the kidney drainage system on the kidney ultrasound.

What causes prenatal hydronephrosis?

  • Unknown (idiopathic). In more than half of babies who are diagnosed with hydronephrosis before birth, the condition goes away on its own and the cause is never known.

  • Ureteropelvic junction (UPJ) obstruction is a blockage where the kidney meets the ureter (the tube that carries urine from the kidney to the bladder). This leads to a buildup of urine in the kidney.

  • Ureterovesical junction (UVJ) obstruction is a blockage where the bladder meets the ureter (tube that carries urine from the kidney to the bladder). This leads to a buildup of urine in the kidney.

  • Posterior urethral valves (PUV) is a form of blockage of the kidney's drainage system that happens only in boys. It is caused by a blockage in the urethra, the tube that carries urine from the bladder through the penis

  • Ureterocele is when the ureter does not develop properly and causes a small pouch or bulge into the bladder

  • Vesicoureteral reflux (VUR) is when urine in the bladder flows backwards into the ureters and sometimes into the kidneys

  • Ectopic ureter is an attachment of the ureter to somewhere outside the bladder, like the urethra or vagina

  • Neurogenic bladder is when the nerves do not properly carry the message from the bladder to the brain and from the brain to the muscles of the bladder.

  • More rare causes of hydronephrosis include urethra atresia (when the drainage tube from bladder did not develop properly) or bladder neck obstruction (a blockage that reduces or stops urine flow out of the bladder)

How is hydronephrosis diagnosed?

Hydronephrosis is most commonly diagnosed on a routine prenatal ultrasound. In these cases, an ultrasound is done after birth to see if hydronephrosis persists. It is important that an ultrasound is done at least 48 hours after birth. This is because an ultrasound within the first two days of life can show a falsely low level of hydronephrosis.

How is the cause of hydronephrosis diagnosed?

Many children have mild or no hydronephrosis on the ultrasound after birth. They may not need any more testing.

Children with moderate or severe hydronephrosis after birth may need other tests. These tests, which may include a voiding cystourethrogram or nuclear medicine renal scan, can look for vesicoureteral reflux, posterior urethral valves or blockages like UPJ or UVJ obstruction.

What are the signs & symptoms of hydronephrosis?

Most children with hydronephrosis have no symptoms. However, children with hydronephrosis may be at higher risk for urinary tract infections (UTIs). Symptoms of a UTI may include fever, burning with urination, cloudy urine, a strong or sudden urge to use the bathroom, back pain or vomiting. Symptoms of UTIs in babies may include irritability, poor feeding or fever. If a UTI is suspected, it's best to get a urine sample using a catheter to decrease the chance of contaminating the urine.

When should I call the doctor?

  • Fever (any temperature greater than 101.5° F) at any age

  • Severe pain in the belly, side or lower back

  • Pain with urination

  • Blood in the urine

  • Persistent irritability and poor feeding in babies

What is the treatment for hydronephrosis?

Hydronephrosis will most often get better on its own with no treatment.

Most cases of mild and moderate hydronephrosis need only periodic monitoring with kidney and bladder ultrasounds. The ultrasounds will show the degree of hydronephrosis and whether it is stable, improving or worsening. They can also monitor the growth of the kidneys over time.

If a child's hydronephrosis is severe or worsens over time, medical intervention may be needed. Some children take a low dose of an antibiotic to help prevent urinary tract infections. The decision for using antibiotics will be made depending on your child's cause of hydronephrosis, which the doctor will discuss with you.

In some cases, children may need to be referred to a kidney doctor (pediatric nephrologist). Blood tests are needed sometimes to know how well the kidneys are working. Some children may need to be referred to a kidney surgeon (pediatric urologist). Sometimes, a procedure is done to repair the blockage in the kidney, or to repair the blockage in the ureter and reconnect it to the healthy portion of the kidney's drainage system. In some cases of VUR, a procedure may be done to prevent the backward flow of urine. Boys with posterior urethral valves may need surgery to remove the blockage in the urethra, which carries urine from the bladder through the penis.

Some urology surgeries can be done with cystourethroscopy, a procedure performed by passing a camera into the urethra and bladder that require no incisions. But others are more traditional surgeries and can be done through one open incision, or with laparoscopic or robotic surgery (through several small incisions).

What are the possible long-term effects of hydronephrosis?

In some cases, hydronephrosis that is severe or left untreated can cause urinary tract infections, kidney scarring, and loss of kidney function that may cause long-term problems.

However, most children with hydronephrosis lead normal lives. Most cases resolve within a child's first few years, often without need for surgery. Even children with hydronephrosis that does not resolve quickly typically do not have kidney damage and have no long-term problems.

More Information

About Dr. Weidemann

Pediatric nephrologist Darcy Weidemann, MD, FAAP, is a member of the American Academy of Pediatrics (AAP) Section on Nephrology. She is an Associate Professor of Pediatrics, University of Missouri-Kansas City School of Medicine.

About Dr. Kupferman

Juan C. Kupferman, MD, MPH, FAAP, is board certified general pediatrics and pediatric nephrology. He serves on the AAP Section on Nephrology Executive Committee, is Chief of Pediatric Nephrology and Hypertension at Maimonides Medical Center in Brooklyn. Dr. Kupferman is also a Professor of Pediatrics at Albert Einstein College of Medicine and Adjunct Professor at SUNY Downstate.

Last Updated
American Academy of Pediatrics, American Society of Pediatric Nephrology and the National Kidney Foundation Patient Education Collaborative (Copyright © 2022)
The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
Follow Us