Multicystic dysplastic kidney (MCDK) is a condition in which one or both of a baby’s kidneys do not develop normally while the baby is growing in the womb. Fluid-filled sacs, called cysts, replace normal kidney tissue and prevent the affected kidney from working.

When only one kidney is affected, the unaffected kidney usually grows larger to compensate for the nonworking kidney, and it does the work of both kidneys. The nonworking kidney usually shrinks and disappears over time. The remaining, working kidney is called a solitary or single-functioning kidney. A health care professional may need to evaluate the unaffected kidney to make sure it is working properly.

Babies born with MCDK in only one kidney can grow normally and may have few, if any, health problems. Babies born with MCDK in both kidneys may not survive long after birth. Babies who do survive often develop kidney failure and require kidney replacement therapy—dialysis or a kidney transplant.

MCDK is different from polycystic kidney disease, which is a disorder that causes fluid-filled cysts to grow in the kidneys.

A small study estimated that between 1 in 1,000 babies and 1 in 4,300 babies are born with MCDK each year. However, some babies with MCDK are never diagnosed with the condition, so researchers don’t know exactly how many people have MCDK.

MCDK is more likely to occur in babies or fetuses who have

• parents with genetic traits for the condition
• certain genetic syndromes that affect multiple parts of the body

MCDK is more common in boys than in girls.

MCDK is a birth defect that happens when the fetus is developing in the womb. Researchers don’t know exactly what causes MCDK, but it may be caused by

• gene mutations that can pass from parent to child, although a genetic cause is usually not found
• genetic syndromes that affect more than one system in the body, such as the digestive system, nervous system, heart and blood vessels, muscles and bones, or other parts of the urinary tract

Many babies born with MCDK in only one kidney have no signs of the condition. In some babies, the affected kidney may be bigger than normal at birth and may cause pain.

Most often, MCDK is diagnosed before birth, during a prenatal ultrasound. Ultrasounds use sound waves to create a picture of how a baby is developing in the womb. The images can show problems with the fetus’s kidneys and other parts of the urinary tract. Ultrasounds during pregnancy are part of regular prenatal testing. After the baby is born, a health care professional will perform an ultrasound on the baby to confirm the diagnosis.

In some cases, MCDK is diagnosed after a baby is born. Health care professionals may diagnose MCDK when performing an ultrasound on the baby to check for another medical problem, such as a problem with the urinary tract that may be causing urinary tract infections.

Health care professionals may not need to treat MCDK if the baby has no signs of the condition and only one kidney is affected and the other kidney is healthy. However, health care professionals will suggest regular checkups that include

• blood pressure tests
• blood tests to check how well the kidneys are working
• urine tests to look for protein in the urine and check for kidney damage
• regular ultrasounds to monitor for disappearance of the affected kidney and to make sure the other kidney continues to grow and stay healthy

In rare cases, if the affected kidney doesn’t shrink over time, your child’s health care professional may recommend surgery to remove the nonworking kidney if it is causing problems, such as high blood pressure or kidney infections.

If both kidneys are affected or the healthy kidney becomes damaged, your child may need kidney replacement therapy—kidney transplant, hemodialysis, or peritoneal dialysis—to stay healthy.

If your child’s health care professional suspects your child has kidney disease, you may be referred to a pediatric nephrologist—a doctor who specializes in treating kidney disease in children.

Some children with MCDK may develop high blood pressure, also called hypertension.

Children with MCDK in one kidney may have other urinary tract problems that affect their working kidney. These problems may increase the child’s risk of developing chronic kidney disease.

Researchers have not yet found a way to prevent MCDK.

Researchers have not found that eating, diet, and nutrition play a role in causing or preventing MCDK.

If your child’s kidney function is reduced, your child’s health care professional may suggest changes to what your child eats and drinks to slow the progress of the kidney disease in the unaffected kidney. Talk with your child’s health care professional before making any changes to your child’s diet. Your child’s health care professional may suggest you work with a registered dietitian to create an eating plan with the right foods and nutrients in the right amounts for your child to stay healthy.