Patient education: Prenatal hydronephrosis (The Basics)

What is prenatal hydronephrosis? — "Prenatal" means that a condition happens during pregnancy, when a baby is in the mother's uterus. Prenatal hydronephrosis is a condition that involves one or both of the baby's kidneys (figure 1). Kidneys work to make urine. Each kidney has 2 parts:

●A part that filters the blood – This part removes waste and excess salt and water, leading to the formation of urine.

●A part that collects the urine – This part then sends the urine down the urinary tract, which includes the bladder.

In hydronephrosis, the part of the kidney that collects the urine has too much urine in it. This causes it to swell and get bigger than normal.

Some babies have hydronephrosis that lasts only for a short time and then goes away. This condition is not serious and doesn't cause any long-term problems.

If the hydronephrosis doesn't go away, it could be caused by a serious problem in the urinary tract. For example, there might be a blockage in the urinary tract, or urine might flow backwards from the bladder to the kidney.

How do I know if my baby has prenatal hydronephrosis? — Doctors find out a baby has it when they do a routine imaging test, called an ultrasound, to check on the baby during pregnancy. An ultrasound creates pictures of the baby inside the uterus. Prenatal hydronephrosis does not cause any symptoms.

Will I need more tests? — Yes. If your baby has hydronephrosis, your doctor will want to see if it goes away or not, or gets worse. You will have one or more ultrasounds to follow up during your pregnancy.

When your doctor does an ultrasound, they will check:

●If one or both kidneys have hydronephrosis

●How severe the condition is

●Your amniotic fluid – Amniotic fluid is the fluid in the uterus that surrounds the baby. It is made up of the baby's urine. If a problem keeps the kidneys from making enough urine, the amount of amniotic fluid will be low.

If the follow-up ultrasound shows that the hydronephrosis has gone away, you probably won't need any more tests.

If the follow-up ultrasound shows that the hydronephrosis has not gone away or is worse, you will likely need more tests. These can include more ultrasounds or tests to look for other conditions.

How is prenatal hydronephrosis treated during pregnancy? — Doctors follow the condition with tests, but they do not usually treat it.

How is hydronephrosis treated after birth? — It depends on the number of kidneys involved and how severe the condition was before birth.

If the hydronephrosis went away before birth, your baby will not need any tests or treatment after birth.

If the hydronephrosis did not go away, your baby will need tests after birth. They might also need treatment.

●If the condition involved only one kidney or was mild, your baby will have an ultrasound after they are 1 week old. Depending on those results, they might need other tests. Your baby's doctor might also prescribe an antibiotic medicine. This medicine can help prevent your baby from getting a kidney infection.

●If the condition involved both kidneys or was severe, your baby will have an ultrasound within the first few days of life. Your baby's doctor will probably prescribe an antibiotic medicine. This medicine can help prevent your baby from getting a kidney infection. Your baby might also need other tests to check the urinary tract.

More on this topic

Patient education: Amniocentesis (The Basics)
Patient education: Chorionic villus sampling (The Basics)

Patient education: Urinary tract infections in adolescents and adults (Beyond the Basics)