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Fetal Pyelectasis or Pelviectasis

Fetal pyelectasis or pelviectasis typically consists of a mild enlargement of the central area, or “pelvis,” of the kidney. (This is not to be confused with fetal hydronephrosis, which is an extreme ballooning of the kidney.) The increase in size may be the result of urine not being able to flow freely from the kidney to the bladder, which is known as ureteropelvic junction obstruction (UPJO)​; this causes the pelvis of the kidney to stretch from pressure. Urine can also back up from the bladder into the kidneys; this is known as reflux. In the absence of an active kidney infection, reflux does not cause pain, problems with urination or any other symptoms.

It is also possible that one of the baby's kidneys may be normal but simply larger than average. If the enlargement is due to pelviectasis, it is medical concern; but sometimes a larger-than-average kidney may simply be a normal variable — a factor of a person's family genetics.

This is a good example of a situation in which new, highly accurate instruments allows physicians to see and measure something in the fetus, but it is not yet clear where the line between "normal" and "a problem" is drawn. Fetal pelviectasis/pyelectasis is a finding — not a problem by itself.

To address this situation — that is, finding out if the small increase in size is the result of a problem or just a normal finding in a given baby — many doctors do periodic sonograms to observe the size of the kidney pelvis, the length of the kidney, the size of the bladder and the appearance of the kidney tissue itself. Following these changes through the pregnancy appears to give the most useful answer to the question "is it normal?"

Often the ultrasound examinations are continued after birth, and sometimes other tests such as a voiding cystourethrogram (VCU) or a renal scan, are done to follow the system's development and health.

To differentiate early pelviectasis, which may be normal, from hydronephrosis, which is an extreme ballooning of the kidney, the term sonographically evident renal pelvis (SERP) has been coined. SERP means that the renal pelvis can be seen with the new, highly accurate sonograms. The term is used to describe the finding, which is not necessarily a problem, so that all caregivers can more easily understand its significance.

Fetal pyelectasis is found in approximately 1% of all pregnancies, which makes it a relatively common finding. It is more often seen in male fetuses than female.

Diagnosis & ​Treatment

Fetal pelviectasis/pyelectasis is diagnosed by ultrasound (sonogram) examination before birth. Evaluation of the kidneys is part of the routine ultrasound examination done by many obstetricians as part of their prenatal care around the 20th week of pregnancy. Specialists in the Institute for Fetal Health can consult parents expecting a child with fetal pelviectasis/pyelectasis.

Pyelectasis is a finding on an ultrasound examination and requires follow-up but not necessarily treatment as we have discussed. Frequently, the finding disappears by itself and does not have any negative impact on the baby. However, infants with pyelectasis are more prone to other urological problems, especially if the urine does not drain and continues to increase in the kidneys throughout the pregnancy. When the size increase is the result of pressure from obstructed urine flow, surgery to correct the obstruction is often necessary after birth.

Long-ter​m Effects

Ultrasound follow up after birth and other tests can identify those babies for whom fetal pyelectasis/pelviectasis is part of a serious problem. When these tests show no problem in the urinary system, the babies do very well.


Research is underway at Lurie Children’s to evaluate the long-term implications of fetal pelviectasis/pyelectasis when no problem is identified — an area not previously studied.