Fetal Renal Pelvis Dilatation

The ureter is a narrow tube which drains urine from the kidneys to the bladder. Where the ureter meets the kidney is called the renal pelvis. This normally measures less than 4mm at the 19-21 week morphology scan.

In 1-2% of pregnancies the renal pelvis of the baby is dilated to around 4-10mm. This can be seen and measured at the mother’s 19-21 morphology scan. In most cases fetal renal pelvis dilatation is a normal variation which resolves in later pregnancy or shortly after delivery.

In some babies however, the dilatation may be due to reflux of urine or rarely obstruction of the ureter. Both of these conditions are treatable.

Where there is reflux, the urine flushes back up the ureters towards the kidneys each time the baby contracts its bladder to pass urine. In the majority of cases this resolves with time as the baby gets older and the valve mechanism between the bladder and ureters matures. With some babies however a short course of antibiotics is needed and only rarely is surgery performed to correct the problem.

With obstruction, the ureter may be partially blocked anywhere along its length from the kidney to the bladder. In the vast majority of babies the obstruction is mild and surgery is not required.

It is important to perform a follow up ultrasound at 28-32 weeks in all babies with renal pelvis dilatation in order to identify those who will require treatment for related problems in the future. In the majority of these babies no long term kidney damage results.