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Fetal pregnancy complications


Types of Abdominal Wall Defects : Explaining Gastroschisis and Omphalocele

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Pyelectasis, or renal pelvic dilation, is swelling of the renal pelvis due to:

  • An accumulation of liquid in the pelvis
  • An increase of pressure in the pelvis
  • An obstruction in one or both kidneys of the fetus

This affects between 2% to 5% of all pregnancies.

When the buildup of fluid or the increase in pressure is severe, it can also cause dilation of the calyxes and sometimes even the ureters. This can lead, in extreme cases, to a decrease in the volume of amniotic fluid.

Normal renal pelvis measurements

  • Before week 20 = less than 4 mm
  • Between weeks 20 and 32 = less than 7 mm
  • After week 32 = less than 10 mm

Bilateral pyelectasis associated with other fetal malformations can be a marker for trisomy 21. Genetic counselling is needed to rule out this risk with amniocentesis.


Isolated pyelectasis can be caused by an obstruction in the ureter. This obstruction is often due to a stricture (narrowing) or partial blockage of the ureter.

Vesicoureteral reflux, especially in boys, can also be the cause.

Tests and procedures

A referral to a university hospital centre is recommended in order to establish a diagnosis.

Consultation with the pediatric nephrology team may also be necessary depending on the extent of the pyelectasis.

Treatments and follow up

An assessment of the unborn baby is made by a multidisciplinary team made up of an obstetrician specializing in maternal-fetal medicine, a geneticist, a nephrologist and/or urologist, a radiologist, and a clinical nurse.

In most cases, childbirth does not have to take place at CHU Sainte-Justine. The baby can be delivered at another birthing centre and postnatal care by our team of nephrologists/urologists can be organized for postnatal care.

Resources and useful links

Robert K. Creasy & Robert Resnik, Maternal-Fetal Medicine: Principle and Practice, 7th edition, Milton: Elsevier, 2014.

Page by

Dr Véronique Phan, Dr Lucie Morin, Chantal Larcher, inf. clinicienne

About this page
Updated on 1/25/2021
Created on 1/25/2021
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