Kidneys with Dilated Collecting Systems

As you know, an ultrasound scan has shown that your baby has a minor problem with their kidneys. This leaflet aims to tell you more about it.

What is the problem?

The collecting systems of your baby’s kidney appear a little larger than expected. The collecting system is the set of tubes that gather the urine produced by the kidney; this then trickles down another tube (the ureter) to the bladder. The baby then passes the urine out into the amniotic fluid.

The appearance may be normal for your baby, or it may be that there is some disruption to this flow of urine. Either the urine is held back or it ‘backtracks’ up the ureter into the kidney. This can cause the tubes to become enlarged or dilated.

Why does it occur?

It may be that when your baby’s kidneys were formed very early in pregnancy there was a minor error in the way the ureter or bladder was formed. This can lead to an abnormal flow of urine between the kidneys and the bladder, or to dilatation of these tubes.

How common is it?

This is one of the most common problems seen on ultrasound at the 20-week fetal anomaly scan. It occurs in approximately 1% of pregnancies.

Will my baby have other abnormalities?

Usually this is an isolated finding, but very occasionally, kidney problems can be associated with an underlying condition in the baby, and we will discuss with you whether any further investigations are appropriate. We will look very carefully at the rest of your baby during a scan, and we will discuss any other concerns with you.

Will this affect my baby during pregnancy?

It is unlikely that this will affect your baby during pregnancy. In a small number of babies, the collecting system continues to get bigger, but we do not usually need to change your plans for pregnancy and birth.

We will arrange to scan you again later on in the pregnancy (around 32 weeks), to see if the appearances have changed. Sometimes the collecting systems look normal at this later scan; this is reassuring and no further follow up will be required If the collecting systems remain enlarged, we will suggest that your baby has their kidneys scanned after birth.

Will this condition affect my baby’s future life?

In most cases, it is not likely to have any effects on your baby. Occasionally however, there is a chance that the baby could be more likely to have urinary tract infections, which if left untreated could cause some kidney damage.

If the collecting system of the kidneys still looks enlarged after birth, your baby may need to have further tests to find out why the collecting systems look the way they do, and to see if any treatment is needed. Each baby is different, and we will always discuss what our findings may mean for your baby at each stage.

It is important that you make sure whoever examines your baby after birth is aware of the possible problem, so that they can organise a scan. We will place a label on your hand-held notes to remind those staff who are looking after you.

If you have any questions about what we have said, please do not hesitate to contact the Ultrasound Department on 01305 254530. Your GP, midwife or obstetrician may also be able to give you more information.

About this leaflet

Author: Alison Bromley, Superintendent Sonographer
Written: August 2018
Approved and updated: May 2025
Review date: May 2028
Edition: v2

If you have feedback regarding the accuracy of the information contained in this leaflet, or if you would like a list of references used to develop this leaflet, please email patientinformation.leaflets@dchft.nhs.uk