What is fetal megacystis?
Fetal megacystis means that your baby’s bladder is larger than normal in early pregnancy. It is usually seen on the first trimester scan. In some cases, it can be a sign of a problem with how the baby’s urinary system is developing.
It is seen on an ultrasound scan, usually between 11–14 weeks. The bladder appears large and may take up more space than usual.
Fetal megacystis happens when the baby’s bladder does not empty properly and becomes stretched or enlarged.
Possible causes include:
- A temporary delay in bladder development – in some babies, the bladder looks big early in pregnancy but later becomes normal.
- A blockage in the urinary system – for example, a narrowing or valve in the tube that drains urine from the bladder (called posterior urethral valves) in boys.
- Problems with the nerves or muscles that control the bladder.
- Chromosome or genetic conditions, which can sometimes affect how the urinary system develops.
Your fetal medicine team will do detailed scans and may offer further tests to find out the cause and what it might mean for your baby.
It depends on how large the bladder is and whether other problems are found. Some babies with mild megacystis develop normally. In other cases, it can lead to more serious complications, like kidney or lung problems.
The outcome for babies with fetal megacystis can vary depending on the cause and how severe it is:
- In some cases, especially if the bladder is only slightly enlarged, it can get better on its own as the baby grows.
- If the bladder remains very large or there is a blockage, it can stop urine from leaving the bladder. This can affect how the baby’s kidneys and lungs develop.
- Some babies may need specialist care after birth, and in certain cases, surgery may be needed to help the bladder drain properly.
Your fetal medicine team will talk you through what this means for your baby and arrange regular scans to check the bladder, kidneys, and fluid around the baby (amniotic fluid).
If your baby is found to have a large bladder, you will be referred to a fetal medicine specialist for more detailed checks.
- You will have a detailed ultrasound scan to look closely at the baby’s bladder, kidneys, and other organs.
- The team will check for the cause of the megacystis and see if it is mild or severe.
- You may be offered invasive tests to check for any chromosome or genetic conditions.
- The amount of amniotic fluid will be monitored closely, as it helps show how well the baby’s kidneys are working.
- You will have regular scans throughout the pregnancy to see if the bladder changes in size or if there are any signs of blockage.
- Your specialist team will support you in understanding the findings, what they mean for your baby and gently guide you through the choices ahead.
In most cases, fetal megacystis happens by chance and is unlikely to happen again in future pregnancies . If a genetic condition is found, you may be offered counselling about future risks.