Fetal Renal Pelvis Dilatation (RPD)

What is renal pelvis dilatation?

Renal pelvis dilatation (RPD) is a condition where the part of the kidney that collects urine (the renal pelvis) is larger than usual. It is commonly seen on a pregnancy ultrasound and may go away on its own.

There are two types of RPD.

Unilateral renal pelvis dilatation 
This means only one kidney is affected. 
Most babies with one enlarged kidney grow and develop normally, and the condition often gets better on its own before or soon after birth. 
Bilateral renal pelvis dilatation 
This means both kidneys are affected. 
When this happens, doctors will look more closely to make sure the baby’s urinary system is draining properly and that the amniotic fluid levels are normal. Babies with both kidneys affected may need closer monitoring and sometimes extra tests after birth.

How is RPD diagnosed?

It is usually diagnosed during the 20-week scan. The scan shows that the renal pelvis is wider than expected for your baby’s stage of development.

What causes RPD?

There are a few possible causes for RPD:

-  Normal variation: In many babies, a small amount of widening is normal and often goes away on its own as the baby grows.

-  Slow urine drainage: Sometimes urine drains more slowly from the kidney into the bladder, causing temporary swelling.

-  A blockage: There may be a narrowing or obstruction somewhere in the urinary system.

-  Reflux (backflow of urine): Urine may flow backwards from the bladder up towards the kidney.

-  Other kidney or urinary tract differences : Occasionally, RPD can be linked to other conditions affecting how the urinary system develops.

Your fetal medicine team will monitor your baby’s kidneys with ultrasound scans and may recommend additional tests if the widening increases or affects both kidneys.

What does it mean for my baby?

In most cases, especially if mild, it does not cause problems and resolves before or after birth. If moderate or severe, your baby may need follow-up scans and possibly treatment after birth.

What happens next?

You may have additional scans during pregnancy to check if the dilatation gets better, worse, or stays the same. After birth, your baby may have an ultrasound and may be referred to a kidney specialist.

If renal pelvis dilatation (RPD) is seen on your baby’s scan, you will usually be referred for follow-up care with fetal medicine team.

Here’s what usually happens next:

-  Follow-up scans: You will have regular ultrasound scans during pregnancy to check if the widening gets better, stays the same, or increases.

-  Check both kidneys: The scans will look closely at both kidneys, the bladder, and the amniotic fluid (the fluid around your baby), as this helps show how well the urinary system is working.

-  Monitor the pregnancy: In most cases, RPD stays mild or goes away on its own before birth. If it increases or affects both kidneys, your care team will keep a closer watch.

What happens after my baby is born

-  Your baby may have a kidney ultrasound within the first few days or weeks of life to see if the RPD is still present and prophylactic antibiotics (a small daily dose of antibiotics) may be offered to help prevent urinary tract infections (UTIs). Your baby’s doctor or specialist team will explain if antibiotics are recommended and for how long. Not all babies with RPD need them.

-  Further tests: If the widening continues after birth, your baby may be referred to a paediatrician or kidney specialist (paediatric nephrologist or urologist) for further checks or tests.

-  In most cases, babies with RPD do very well and do not need any treatment, but ongoing monitoring helps ensure their kidneys stay healthy.

Will this happen again?

Most cases are not inherited and don’t occur again. If a genetic condition is suspected, you may be offered genetic counselling.