What Does Enlarged Renal Pelvis Mean?


Dear Ms Ultrasound,
I had an appointment with my OB today and he told me that an ultrasound I had 2 weeks ago showed that my baby was presenting a slightly enlarged kidney. I am 35 weeks and 3 days pregnant now and was 33 weeks and 3 days at the time of the ultrasound.

My doctor told me this was very common and not to worry. He explained that an ultrasound showing this in the baby's renal pelvis is very common. However, I looked on your website and read your answer on the same topic which said pretty much the same thing. I noticed that you said 5 mm and under is normal and that is what made me curious. My baby's measurement was 4mm, so I don't understand why the ultrasound came back with that notation. Is it that one kidney is larger than the other? Should I be concerned?


Hi, I'm glad you got the information from a previous answer. The reason the measurement of the renal pelvis was noted, is because we usually don't really see the renal pelvis large enough to measure. If it is large enough to measure, it will be measured. This is what's termed a prominent renal pelvis. It is measured and noted on the report sent to your doctor.

This finding is fairly common and entirely within the limits of normal. What usually happens is a second ultrasound will be ordered to make sure that the renal pelvis has not widened. I like to look at these follow-up ultrasounds, as more opportunities to get another baby picture!

Don't worry. Everything you have told me is within the normal parameters.

-- Jane, RDMS

Jane Foley

Jane Foley has worked as a Sonographer (Ultrasound Technologist) since 1979. Jane has lived and worked in many parts of the world including Saudi Arabia. She is a Registered Diagnostic Medical Sonographer or RDMS. She pulls a wealth of information from her experience in the field of Radiology and her interactions with such a broad cross-section of cultures she has visited. She now makes her home on the island of Maui with her English husband, Michael.