My Baby Has a Multicystic Dysplastic Kidney (MCDK)
Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist
Content reviewed against published NIH, AAP, Children's Hospital guidelines
Last reviewed:
If your baby has been diagnosed with or you suspect has a multicystic dysplastic kidney (mcdk), here is what the evidence says.
The short answer
A multicystic dysplastic kidney (MCDK) is a non-functioning kidney that has been replaced by multiple cysts of varying sizes. It is usually found on prenatal ultrasound and is one of the most common kidney anomalies detected before birth. When only one kidney is affected (unilateral), the other kidney compensates and provides normal function. The MCDK typically shrinks (involutes) and may disappear entirely by age 5. No treatment is needed for unilateral MCDK beyond periodic monitoring with ultrasound. Bilateral MCDK is fatal. There is a small increased risk of problems in the normal opposite kidney, so both kidneys are monitored.
Key takeaways
- A multicystic dysplastic kidney (MCDK) is a non-functioning kidney that has been replaced by multiple cysts of varying sizes. It is usually found on prenatal ultrasound and is one of the most common kidney anomalies detected before birth. When only one kidney is affected (unilateral), the other kidney compensates and provides normal function. The MCDK typically shrinks (involutes) and may disappear entirely by age 5. No treatment is needed for unilateral MCDK beyond periodic monitoring with ultrasound. Bilateral MCDK is fatal. There is a small increased risk of problems in the normal opposite kidney, so both kidneys are monitored.
- Usually normal when: MCDK was diagnosed prenatally or postnatally, the opposite kidney is functioning normally, and your baby is growing well
- Call your doctor if: Your baby has a fever with no obvious source - a UTI must be ruled out promptly to protect the single functioning kidney
- Varies by age — see the age-by-age breakdown below
“Fever itself is not an illness — rather, it is a sign or symptom that the body is fighting an infection. Fever stimulates certain defenses, such as the white blood cells, which attack and destroy invading bacteria.”
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What Parents Should Know
According to NIH, AAP, Children's Hospital guidelines, a multicystic dysplastic kidney (MCDK) is a non-functioning kidney that has been replaced by multiple cysts of varying sizes. It is usually found on prenatal ultrasound and is one of the most common kidney anomalies detected before birth. When only one kidney is affected (unilateral), the other kidney compensates and provides normal function. The MCDK typically shrinks (involutes) and may disappear entirely by age 5. No treatment is needed for unilateral MCDK beyond periodic monitoring with ultrasound. Bilateral MCDK is fatal. There is a small increased risk of problems in the normal opposite kidney, so both kidneys are monitored. At Prenatal, mCDK is typically diagnosed on a routine prenatal ultrasound. The affected kidney appears as a cluster of cysts of various sizes with no normal kidney tissue visible between them, distinguishing it from hydronephrosis (which shows a central dilated collection). The opposite kidney should be evaluated carefully, as there is a 15-30% chance of associated anomalies (such as vesicoureteral reflux or UPJ obstruction) in the contralateral kidney. Amniotic fluid levels are usually normal when one kidney functions properly. It is generally considered normal when mCDK was diagnosed prenatally or postnatally, the opposite kidney is functioning normally, and your baby is growing well. However, you should contact your pediatrician promptly if your baby has a fever with no obvious source - a UTI must be ruled out promptly to protect the single functioning kidney.
Normal vs. Concerning
When to Seek Immediate Care
- Your baby has a fever with no obvious source - a UTI must be ruled out promptly to protect the single functioning kidney
- Your child has blood in the urine, abdominal pain, or signs of a kidney infection (high fever, back pain, vomiting)
- Your child has significantly decreased urine output, which may indicate a problem with the functioning kidney
- The MCDK appears to be growing significantly on follow-up ultrasound rather than involuting, which is rare but warrants further evaluation
By Age
What to expect by age
Prenatal
MCDK is typically diagnosed on a routine prenatal ultrasound. The affected kidney appears as a cluster of cysts of various sizes with no normal kidney tissue visible between them, distinguishing it from hydronephrosis (which shows a central dilated collection). The opposite kidney should be evaluated carefully, as there is a 15-30% chance of associated anomalies (such as vesicoureteral reflux or UPJ obstruction) in the contralateral kidney. Amniotic fluid levels are usually normal when one kidney functions properly.
0-1 month
After birth, a renal ultrasound confirms the diagnosis and evaluates the opposite kidney. A VCUG (voiding cystourethrogram) is often performed to check for vesicoureteral reflux in the contralateral kidney, since reflux is found in about 15-25% of cases. Kidney function tests are usually normal since the normal kidney compensates. Your baby will be referred to a pediatric urologist or nephrologist. Blood pressure monitoring begins at routine well-visits.
1-12 months
Your baby with unilateral MCDK will grow and develop normally. The multicystic kidney is non-functioning and will gradually shrink over time. Follow-up ultrasounds are typically done periodically (every 6-12 months initially) to monitor both the involuting MCDK and the health of the opposite kidney. As with any child with a solitary functioning kidney, prompt evaluation of unexplained fevers is important to rule out UTI and protect the working kidney.
1-5 years
By this age, the MCDK has often significantly decreased in size and may no longer be visible on ultrasound. The opposite kidney continues to compensate by growing larger. Follow-up ultrasounds are usually spaced further apart (every 1-2 years). Historically, nephrectomy (removal of the MCDK) was sometimes performed, but current practice is conservative since the MCDK involutes on its own and the risk of malignancy arising from an MCDK is extremely low.
5 years+
Long-term outcomes for unilateral MCDK are excellent. Most children have completely normal kidney function using their single working kidney. The main considerations are the same as for any person with a solitary functioning kidney: monitoring blood pressure, protecting the kidney from injury, treating UTIs promptly, and staying well-hydrated. Follow-up imaging may continue periodically, but many children can be transitioned to routine pediatric care with periodic blood pressure checks.
What to Tell Your Pediatrician
- Describe when you first noticed has a multicystic dysplastic kidney (mcdk) and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if you have questions about the difference between MCDK and polycystic kidney disease.
- Mention if you are concerned about the size of the MCDK or it appears to be growing rather than shrinking on ultrasound.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
What Should You Do?
When to take action
- MCDK was diagnosed prenatally or postnatally, the opposite kidney is functioning normally, and your baby is growing well
- Follow-up ultrasounds show the MCDK is stable or shrinking (involuting) over time
- Kidney function tests are normal
- Blood pressure is normal at routine checks
- Your baby has no urinary symptoms and is meeting all developmental milestones
- You have questions about the difference between MCDK and polycystic kidney disease
- You are concerned about the size of the MCDK or it appears to be growing rather than shrinking on ultrasound
- Your child has had a UTI and you want to discuss how to protect the functioning kidney
- You are wondering about activity restrictions or contact sports for your child
- Your baby has a fever with no obvious source - a UTI must be ruled out promptly to protect the single functioning kidney
- Your child has blood in the urine, abdominal pain, or signs of a kidney infection (high fever, back pain, vomiting)
- Your child has significantly decreased urine output, which may indicate a problem with the functioning kidney
- The MCDK appears to be growing significantly on follow-up ultrasound rather than involuting, which is rare but warrants further evaluation
What You Can Do at Home
- Keep track of when you notice has a multicystic dysplastic kidney (mcdk) — noting the time of day, duration, and any triggers can help your pediatrician.
- Remember that mCDK was diagnosed prenatally or postnatally, the opposite kidney is functioning normally, and your baby is growing well — this is generally within the range of normal.
- At Prenatal, focus on observation rather than intervention unless your pediatrician advises otherwise.
- Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
- While monitoring at home, seek immediate care if your baby has a fever with no obvious source - a UTI must be ruled out promptly to protect the single functioning kidney.
Related Conditions
20-Week Anatomy Scan Unexpected Findings
The 20-week anatomy scan checks your baby's major organs, structures, and growth. Most scans are completely normal. When unexpected findings are identified, they range from minor variants that resolve on their own to conditions that need further evaluation. Many findings require nothing more than a follow-up ultrasound to confirm the baby is developing well.
My Baby Has Polycystic Kidney Disease (PKD)
Polycystic kidney disease (PKD) in children comes in two main forms. Autosomal recessive PKD (ARPKD) typically presents in infancy with greatly enlarged kidneys, hypertension, and liver fibrosis, and can cause respiratory distress at birth from the large kidneys compressing the lungs. Autosomal dominant PKD (ADPKD) is more common overall but usually does not cause symptoms until adulthood, though it can occasionally be detected prenatally or in childhood. Treatment focuses on managing symptoms, controlling blood pressure, and preserving kidney function for as long as possible.
Related Resources
Frequently asked questions
Is has a multicystic dysplastic kidney (mcdk) normal?
When should I call the doctor about has a multicystic dysplastic kidney (mcdk)?
When is has a multicystic dysplastic kidney (mcdk) normal?
What causes has a multicystic dysplastic kidney (mcdk)?
What should I mention to my pediatrician about has a multicystic dysplastic kidney (mcdk)?
Is has a multicystic dysplastic kidney (mcdk) normal at Prenatal?
Is has a multicystic dysplastic kidney (mcdk) normal at 0-1 month?
Should I go to the ER for has a multicystic dysplastic kidney (mcdk)?
Does has a multicystic dysplastic kidney (mcdk) go away on its own?
References
- [1]National Institutes of Health. Multicystic Dysplastic Kidney. Genetic and Rare Diseases Information Center (GARD), 2024. NIH
- [2]Urology Care Foundation. Multicystic Dysplastic Kidney. American Urological Association, 2024. AAP
- [3]Children's Hospital of Philadelphia. Multicystic Dysplastic Kidney (MCDK). Children's Hospital
Doctor Visit Checklist
Bring this checklist to your next pediatrician visit to discuss My Baby Has a Multicystic Dysplastic Kidney (MCDK).
Things to mention
- Describe when you first noticed has a multicystic dysplastic kidney (mcdk) and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if you have questions about the difference between MCDK and polycystic kidney disease.
- Mention if you are concerned about the size of the MCDK or it appears to be growing rather than shrinking on ultrasound.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
Observations to share
- You have questions about the difference between MCDK and polycystic kidney disease
- You are concerned about the size of the MCDK or it appears to be growing rather than shrinking on ultrasound
- Your child has had a UTI and you want to discuss how to protect the functioning kidney
Urgent signs to report immediately
- Your baby has a fever with no obvious source - a UTI must be ruled out promptly to protect the single functioning kidney
- Your child has blood in the urine, abdominal pain, or signs of a kidney infection (high fever, back pain, vomiting)
- Your child has significantly decreased urine output, which may indicate a problem with the functioning kidney
My notes
From ismybabyalright.com — free, evidence-based baby health guides
All content follows our editorial policy and is reviewed against published clinical guidelines.
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Related Resources
Bottom line
Most cases of has a multicystic dysplastic kidney (mcdk) are normal. Talk to your pediatrician if your baby has a fever with no obvious source - a uti must be ruled out promptly to protect the single functioning kidney.
Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.
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20-Week Anatomy Scan Unexpected Findings
The 20-week anatomy scan checks your baby's major organs, structures, and growth. Most scans are completely normal. When unexpected findings are identified, they range from minor variants that resolve on their own to conditions that need further evaluation. Many findings require nothing more than a follow-up ultrasound to confirm the baby is developing well.
My Baby Has Polycystic Kidney Disease (PKD)
Polycystic kidney disease (PKD) in children comes in two main forms. Autosomal recessive PKD (ARPKD) typically presents in infancy with greatly enlarged kidneys, hypertension, and liver fibrosis, and can cause respiratory distress at birth from the large kidneys compressing the lungs. Autosomal dominant PKD (ADPKD) is more common overall but usually does not cause symptoms until adulthood, though it can occasionally be detected prenatally or in childhood. Treatment focuses on managing symptoms, controlling blood pressure, and preserving kidney function for as long as possible.
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