Renal pelvic dilatation in your developing baby

This information should help answer your questions if you had an ultrasound scan at 20 weeks and have been informed that your developing baby has fetal renal pelvic dilatation (RPD).

Renal pelvic dilatation is when the part of your baby's kidneys (called the renal pelvis) is enlarged. In most cases, there is no underlying problem and it might be temporary, often when the baby's bladder is full.

Sometimes, it's because the backward flow of urine (pee) from the bladder into the ureters (the tubes that carries urine from the kidney to the bladder).

Rarely, a delay to the flow of urine may be causing the enlargement (dilatation) seen in the kidneys.

There is no need for any treatment before the baby is born in most cases, but they might need some medicines or tests after they are born.

Renal pelvic dilatation

Each of the kidneys has 2 areas. The first produces urine (pee). The second moves urine from the kidneys to the bladder. This is called the renal pelvis.

Urine flows from the renal pelvis down the tube called the ureter into the urinary bladder. This system is found on both the right and left sides of the body. 

The measurement of the renal pelvis is measured at your 20 week ultrasound scan. The normal measurement of the renal pelvis is:

  • 0 to 7mm before 28 weeks
  • less than 8mm after 28 weeks
  • less than 10mm after 32 weeks

If the measurement is more than this, it is called renal pelvic dilatation.

What happens next

You have a follow-up scan in the fetal medicine unit at about 32 to 36 weeks of pregnancy, or earlier. The renal pelvic dilatation may have gone away by the time of this examination.

You might also see a paediatric urologist (a doctor who looks after children with urinary tract problems) who will explain to you what will happen after your baby is born.

After your baby is born

Your baby might need a small dose of antibiotics to prevent urinary tract infections.

Your baby might need further scans. When you have these scans will be decided by the neonatologists (baby doctors).

If the scans are normal, the doctor will write to you or your GP asking you to stop taking antibiotics.

If the scans show continuing or increasing dilatation, your baby may need further scans or treatment and an appointment will be made to see the paediatric urologist.

Resource number: 3663/VER2
Last reviewed: July 2023
Next review: July 2026

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