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Pregnant. US showed fetal kidney to be dilated. Underlying cause?

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Practicing since : 2005
Answered : 3163 Questions
Good day Doctor.

I am 29 weeks 4 days pregnant. I had an ultrasound scan. During the scan at 3.40 pm, I was told that fetal left and right kidney looks dilated. By the time other organs were checked, it was noted that left kidney appeared normal and in another 10 to 15 minutes right kidney also appeared normal. I was given some 30 to 40 minutes of time to walk as they were trying to get 4D picture of baby's face. Once that scan was done, sonographer rechecked the values and this time right kidney looked dilated. Is it normal that renal pelvis dilate and come back to normal state as part of urination process? How long does it take for urine to get collected in renal pelvis in fetus? Is fetal right kidney dilated because kidney processed and filled urine in the renal pelvis? If so, in my case I could see it getting filled in 30 minutes of time. Is it normal?

I have been having regular ultrasound scan from conception as it is an IVF conception . All throughout kidney and bladder appeared normal.

Scan done - 5th, 7th, 11th, 16th, 20th, 24th, 26th ,29th week.

Other details:
Amniotic fluid is Normal - AFI 14
Baby's weight 1.2 Kg +/- 100 gm
Posted Tue, 24 Sep 2013 in Pregnancy
Answered by Dr. Rhea Chanda 25 minutes later
Brief Answer:
Fetal hydronephrosis

Detailed Answer:

There are no proper data available to answer each of your specific questions. The fetal urine formation is a continuous process. Urine is continuously being formed and excreted by the fetus.

Dilated renal pelvic system is not concerning unless it is persistent. Dilated renal pelvic system in the fetus is called fetal hydronephrosis. It can occur in every 1 in 100 pregnancy. It occurs due to bloackage of the flow of urine into the bladder. Now there are several cause for this like obstruction, reflux, stricture and other medical conditions. Most common cause of obstruction may cannot be diagnosed on ultrasound.

From your history, I get to know that you had a temporary dilatation which eased after some time.
This deesn't mean the fetus has an obstruction. Even something as simple as the fetal position can cause some kinking of the collecting system and cause hydronephrosis.

What needs to be done now, is regular ultrasounds. Since you haven't had a problem in your previous ultrasounds, this needs to be followed up. Regular scan to detect whether the dilatation is seen again. We can plan further treating based on subsequent scan reports. Right now, I wouldn't be very concerned.

Hope this helps. Write back for clarifications.


Above answer was peer-reviewed by
Follow-up: Pregnant. US showed fetal kidney to be dilated. Underlying cause? 2 hours later
Thank You Doctor.

I understand that renal pelvic can be in temporary dilated state but should not be consistently dilated which means that for any human being it will be in dilated state while urine is collected and return back to normal once it moves to bladder. Please correct me if wrong.

There could be possibilities that my next scan could be taken when it is in eased state and not dilated. In case if taken in dilated state, I need to wait and ask the sonographer to recheck kidneys after some time to see if gets eased out.

As the renal pelvic returning to normal size, does that mean there is no reflux as well? In case of reflux, will it return back to normal size or will it be slightly dilated? I would like to understand to see if possibility of reflux can be ruled out.

I could understand that there might not be blocks as it is back to normal.
Answered by Dr. Rhea Chanda 16 minutes later
Brief Answer:
None of the causes can be ruled out only by ultrasound

Detailed Answer:
Consistent dilatation of the collecting system would mean there is a pathological cause like strictures, reflux and obstruction. Sometimes if this 'cause' is relieved the dilatation is temporarily resolved and a normal kidney is seen.

Now, in this case, only a temporary dilatation was seen and that too just once. A definitive cause cannot be diagnosed based on ultrasound alone. Further testing by a pediatric urologist is needed to determine the cause for the blockage. Reflux also cannot be ruled out without tests. And as testing done while the fetus is in utero is limited and has some amount of risk, extensive testing can be done after birth unless there is a special need. Pre-natal testing is usually postponed after birth.

Therefore right now, the idea is to have subsequent scan - to note whether the hydronephrosis exists again in the next scans. If it does, repeatedly, then there is obviously a cause behind the block. A decision about testing further can be taken after discussing with pediatric urologist and gynecologist.

I understand this is concerning. I suggest you just wait for your scan. Based on subsequent scan report you can decide the course of action.

Hope this helps.

Above answer was peer-reviewed by
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