Enlarged Kidney in Fetus

An enlarged kidney in fetus happens when a kidney fills up with fluid. Doctors can see it on ultrasound sometime by the 12th week in a pregnancy. It is most often seen in 0.5 percent of female fetuses, and 1 percent of male fetuses. Doctor’s monitor the kidney throughout pregnancy with frequent ultrasounds and then recheck the kidney after the baby is born. In a small number of cases, surgery may be needed. This article will help you understand the causes of this condition, if it is serious, and what can be done about it.

Causes of Enlarged Kidney in Fetus

There are two things that cause enlarged kidney. The first is an obstruction of the urine flow in the urethra or kidney. This keeps the urine from going through to the bladder and out of the body. The second cause is reflux, which occurs when the urine does flow out of the kidney and then back up into the kidney.

Types of Obstruction

  • Posterior Urethral Valve Obstruction – This happens to boys when the tissue that forms the urethra has an abnormality. This obstructs the urine flow in the bladder.
  • Ureteropelvic Junction Obstruction – This happens high up at the point where the ureter and the kidney unite. The ureter at this point can become too narrow to allow urine to pass.
  • Ureterocele – This happens when a part of the ureter develops a bulge. It can affect both the bladder and the kidney.
  • Ureterovesical Junction Obstruction – This obstruction happens lower at the point of the urethra and the bladder entrance.


Vesicoureteral reflux happens as the bladder fills and empties. The muscles connected to the urethra and bladder squeeze the urine back up into the kidney.

Other Reasons for Enlarged Kidney in a Fetus

  • Ectopic Ureter – This is a rare birth defect in which a ureter is connected to the bladder in the wrong place.
  • Cause Not Known – In most cases, there is no cause found and the condition goes away on its own with no complications.

Is It Serious?

During pregnancy, it is actually the baby's urine that replaces needed amniotic fluid. Adequate amniotic fluid levels are important for development of the baby and growth. If there is a urinary tract obstruction and urine cannot pass. This causes amniotic fluid levels to drop and affect the baby. The good news is this only happens in a small amount of cases. Most cases do not need any treatment during pregnancy. The size of the enlarged kidney in fetus, plus amniotic fluid levels will be closely monitored by ultrasound by a doctor known as a perinatologist. They specialize in high risk pregnancies and fetal complications.

What Can Be Done?

If they find an enlarged kidney in your baby, there are things that can be done to monitor or treat the condition. These include:

During Pregnancy


The doctor will do ultrasounds frequently during your pregnancy to check for the following:

  • Kidney development
  • Blockages
  • Kidney size
  • How much amniotic fluid you have


  • If the enlarged kidney in fetus is mild to moderate and does not threaten the pregnancy or your baby’s life, no treatment is needed.
  • In moderate cases where amniotic fluid is low, they can infuse more fluids via amniocentesis through a catheter. 
  • If the condition is severe and threatens the life of your baby, doctors may opt to send you to a specialized hospital for surgery.

After Baby Is Born


Newborns, babies, and kids born with hydronephrosis may be sent to a pediatric urologist to be monitored. Tests include:

  • Kidney ultrasounds to check the size of the kidneys.
  • Voiding cystourethrogram to make sure urine is passing freely.
  • Kidney scans can check for blockages and kidney functions.


If you give birth to a baby with an enlarged kidney, they will most likely take your baby to the NICU (neonatal intensive care unit) for the first few days to watch him/her. Doctor's may put your baby on antibiotics to prevent urinary tract infections while being monitored and your baby may even go home on antibiotics as a means of prevention. The doctor may begin ordering routine ultrasounds to keep checking the kidney or kidneys. The good news is most babies born with this condition go home with mom if they are stable. The doctor will instruct you how to follow-up.

You will most likely have to take your baby for another ultrasound in the near future. A mild case of hydronephrosis may stay mild and not need any attention. Most cases just need good follow-up care and no treatment if watched closely.

If in rare instances the hydronephrosis progresses or causes problems, the doctor will proceed to a voiding cystourethrogram and kidney scan. They may also do an x-ray of the kidneys to see if other structures are complicating the issue. They may also check for urinary tract infections and continue antibiotic use. In some severe and ongoing cases, the doctor may recommend surgery to repair any blockages or issues causing reflux.

Tips and Precautions for Moms

To ensure healthy development of your baby and avoid enlarged kidney in fetus, before you get pregnant:

  • Start taking 400 mcg folic acid daily
  • Quit smoking and drinking alcohol
  • Do not use street drugs
  • Eat a healthy diet

If you are trying to get pregnant, it is a good idea to make healthy lifestyle changes beforehand. You could be pregnant for up to 12 weeks before you know that you are pregnant and this is a critical time for baby's development.

After you find out you're pregnant, do these things during pregnancy to continue healthy development of your baby's tissues:

  • Try avoiding infection
  • Watch your blood sugar levels
  • Eat healthy
  • Take your prenatal vitamins
  • Check any medications with your obstetrician

If you have low amniotic fluid levels due to this condition, your doctor may make further recommendations to help prevent the fluid levels from becoming too low. However, studies show this only helps if the lack of maternal hydration (taking in fluids) contributed to the condition.

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