What is fetal hydronephrosis?

Fetal hydronephrosis is swelling of the kidney caused by a backup of fetal urine.

Hydronephrosis can occur in one kidney (unilateral) or in some cases both kidneys (bilateral). The swelling occurs in the area of the kidney known as the renal pelvis, where urine is stored. 

Hydronephrosis is one of the most common fetal abnormalities diagnosed during pregnancy.


Normally, urine flows down from the kidneys, through the ureters (long narrow tubes), into the bladder, and then out of the body through the urethra.

Fetal hydronephrosis occurs when there is an abnormality in the baby’s urinary tract that prevents this drainage process, causing the urine to back up into the kidney. The abnormality or defect occurs during fetal development.

Hydronephrosis may be caused by:

  • A blockage or obstruction that prevents the outflow of urine. Common blockages include lower urinary tract obstruction (LUTO) commonly caused by the posterior urethral valve, a ureteropelvic junction (UPJ) obstruction, where the top of the ureter connects to the kidney, preventing urine from flowing out of the kidney, or a ureterovesical junction (UVJ) obstruction, where the bottom of the ureter connects to the bladder.
  • Reflux, the backward flow of urine from the bladder up into the kidney. Known as vesicoureteral reflux (VUR), this reverse flow is caused by an abnormal “flap valve” between the bladder and a ureter that allows the backflow of urine or where the fetus has a blockage in the urethra that prevents urine from flowing out of the bladder and into the amniotic sac.

How does fetal hydronephrosis affect my baby?

Hydronephrosis can range from mild to severe. In most cases, the condition is mild and typically has little or no effect on the fetus or newborn baby. More serious cases may require surgery after birth to repair an obstruction or reflux.

In severe cases, hydronephrosis can cause serious complications, including:

  • Too little amniotic fluid, a condition known as oligohydramnios. Fetal urine is the main component of amniotic fluid. If hydronephrosis limits the flow of fetal urine enough to reduce the amniotic fluid below a safe level, it can lead to serious pregnancy complications including underdeveloped lungs and breathing difficulties at birth and deformities of the face and extremities (Potter sequence).
  • Kidney damage and loss of kidney function. The backup of urine puts pressure on the fetal kidneys. This can cause progressive, permanent damage and the risk of kidney failure or rupture.

Hydronephrosis is sometimes graded on a scale of zero to four, zero being no hydronephrosis present and four being the most severe form of the condition.


Hydronephrosis is common, affecting an estimated 1 out of every 100 to 500 babies.

Males are four to five times more likely to develop hydronephrosis than females.


Hydronephrosis is typically diagnosed during a routine ultrasound after the fourth month of pregnancy. It is one of the most common problems detected by prenatal ultrasound screenings.

If hydronephrosis is diagnosed or suspected, you may be referred to a fetal center for a comprehensive evaluation and specialized care.

At Texas Children’s Fetal Center, we arrange for you to visit as quickly as possible to meet with a team of specialists experienced in the diagnosis and treatment of hydronephrosis, including maternal-fetal medicine (MFM) physicians, fetal imaging experts, genetic counselors, neonatologists, and pediatric urologists and nephrologists.

Testing at our center may include:

Following this detailed assessment, our specialists will meet with you about the results, provide treatment recommendations based on your baby’s unique condition, and discuss the potential risks and benefits to help your family make the most informed decisions.

Fetal hydronephrosis

Treatment During Pregnancy

Most cases of hydronephrosis require no treatment during pregnancy, only close observation. You and your baby may have more frequent ultrasounds to monitor the fetal kidneys and amniotic fluid level.

In some cases, fetal hydronephrosis may resolve over time on its own, before birth. Other cases may require surgery after birth to repair the defect in the urinary tract.

In severe cases, where the amniotic fluid level falls to a critically low level, fetal intervention may be an option.

Prior to fetal intervention, a procedure similar to an amniocentesis may be recommended to test kidney function. In this ultrasound-guided procedure, a small needle is inserted into the fetus’ kidney or bladder to obtain a urine sample. The sample is then tested to determine kidney function, and the need for intervention.

Fetal Shunt Placement  

Fetal intervention involves placement of a shunt (hollow tube) in the baby’s bladder or kidney to drain excess urine out into the amniotic sac. The goal is to restore and maintain the amniotic fluid level necessary for fetal lung development, improving the baby’s chance of survival at birth. The shunt may also reduce the pressure inside the fetal bladder and kidneys, preserving kidney function. The shunt, known as a vesicoamniotic shunt, is left in place for the remainder of the pregnancy.

Fetal shunt placement involves serious risks and should be considered only for the most severe cases with the poorest prognosis without treatment.

Is my baby a candidate for fetal intervention?

Hydronephrosis requires highly individualized treatment tailored to the unique needs and condition of each mother and baby. An extensive evaluation is critical to determining if your baby may benefit from fetal intervention.

Our Fetal Center continues to gather data on hydronephrosis patients to establish standards for evaluating which treatments are most successful based on the severity of the condition. These standards look at:

  • The chemistry of fetal urine, to evaluate kidney function
  • Ultrasound evidence of kidney function
  • Amniotic fluid levels
  • Chromosome analysis


We recommend delivery at a hospital with the expertise and resources required to care for pregnancies involving fetal hydronephrosis, including a neonatal intensive care unit (NICU) with breathing support for newborns with underdeveloped lungs, if needed.

Delivery and postnatal care should be carefully planned and coordinated across a team of maternal-fetal medicine, neonatal and pediatric specialists experienced in the care and treatment of hydronephrosis.

Our Fetal Center team works closely with pediatric experts from Texas Children’s Hospital, consistently ranked one of the best children’s hospitals in the nation, providing our patients seamless access to the critical care services and specialists their child may need after birth, avoiding the need for transfers.

Here, the pediatric specialists responsible for treating your child have been an integral part of their care team since before birth.

Treatment After Birth

After birth, Texas Children’s pediatric urologists and nephrologists will conduct additional tests to analyze the structure and function of your baby’s kidneys and bladder.

Testing and treatment may include:

  • Ultrasound of the kidneys and bladder  
  • Blood tests
  • Voiding cystourethrogram (VCUG), an x-ray to evaluate the structure and function of the urinary system
  • Renal (kidney) scan to evaluate the kidneys
  • Antibiotics to prevent or treat urinary infections
  • Surgery to repair an obstruction or reflux

Postnatal Care Team

Your baby’s care team after birth may include:

Why Texas Children’s Fetal Center?

  • A single location for expert maternal, fetal and pediatric care. At Texas Children’s Hospital, you and your baby receive the specialized care required for the diagnosis and treatment of fetal hydronephrosis all in one location, including immediate access to our level IV NICU, avoiding the need to transport a critically ill newborn.
  • A skilled, experienced team with proven outcomes. We have a dedicated team of maternal-fetal medicine specialists, fetal imaging experts, neonatologists, pediatric urologists and pediatric nephrologists who work in concert to care for you and your baby every step of the way, using proven protocols we’ve developed over the years. With their combined expertise and unified approach, this team offers the best possible care for babies with hydronephrosis.
  • We care for your child’s needs at every stage of life. Our comprehensive approach starts with your first prenatal visit and continues throughout your child’s delivery, postnatal care, and childhood, as needed, thanks to one of the nation’s leading teams of fetal and pediatric specialists.

Patient Stories

Thomas's story: Conquering hydronephrosis at Texas Children's

At 24 weeks, we discovered our little guy had hydronephorsis. His bladder was full and the urine was backing up into his kidneys. We were terrified! We searched endlessly for answers, and looked for any hope and help we could find. 

Learn More

For more information or to schedule an appointment,

call Texas Children’s Fetal Center at 832-822-2229 or 1-877-FetalRx (338-2579) toll-free.

Our phones are answered 24/7. Immediate appointments are often available.