Pyelectasis of the fetus, or pelviectasis, is a relatively common condition where urine pools in a fetus’s developing kidney. It’s not a cause for concern, but the condition should be monitored by a medical professional throughout the pregnancy.
You can learn more about pyelectasis in this article. We’ll discuss what to expect and the options available to you if your unborn baby is diagnosed with the condition.
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Pyelectasis is a condition that can affect a developing fetus, where one or both pelves (a central part of the kidney) become larger than normal. This occurs because urine pools in this area.
In a fetus that’s developing normally, urine forms in the kidneys as waste products are filtered from the bloodstream. The urine then travels down the ureter (a tube that connects the kidney to the bladder) before arriving in the bladder. From there, it’s expelled into the amniotic fluid.
When a fetus develops pyelectasis, the urine builds up inside the forming kidney and doesn’t leave.
Any new fetal diagnosis (or finding) can cause alarm if you’re an expectant parent. However, don’t be alarmed if your unborn baby is diagnosed with fetal pyelectasis during your second trimester ultrasound. Only 10% of infants diagnosed with moderate to severe pyelectasis need postnatal intervention and many mild cases clear up on their own.¹
Pyelectasis of the fetus is a common disorder that typically occurs during the second trimester, although the risk extends all the way until birth. Approximately 4.5% of fetuses develop the condition. Males are more likely to experience mild pelviectasis than females.² ³
The condition may affect one kidney (unilateral pyelectasis) or both kidneys (bilateral pyelectasis).
The terms pyelectasis and pelviectasis refer to the enlargement of the renal pelvis (the cavity where urine is collected). On the other hand, the terms pelvicaliectasis and hydronephrosis reference the widening of the calyces (another part of the kidney that collects urine).⁴
In everyday use, these terms are often substituted for one another and employed to describe the expansion of the renal collecting system regardless of the cause.
The term antenatal urinary tract dilation (UTD) is becoming more common as it covers any swelling of the kidney, renal pelvis, ureter, and/or bladder, replacing the more ambiguous terms.
Doctors use measurements taken during the ultrasound, such as the anteroposterior diameter (APD) of the kidney, to determine the severity of the urinary tract dilation.⁵
So what causes pyelectasis of the kidney?
Pyelectasis typically develops for one of two reasons. The first is a blockage of some kind, which prevents the urine from leaving the kidney and traveling to the bladder. This is called ureteropelvic junction obstruction. It might occur due to a narrowing of the ureters or extrinsic pressure from the fetal renal vessels.⁶
Vesicoureteral reflux is another major cause of pyelectasis of the kidney. This occurs when urine flows from the bladder back into the kidneys due to the ureterovesical junction (where the ureter and the bladder meet) not closing properly.⁷
Some genetic conditions, such as Down syndrome, are associated with fetal pyelectasis. However, most cases are not associated with any chromosomal conditions and resolve spontaneously with time.⁸
There is no preventative measure, lifestyle change, or physiological sign that predicts pyelectasis of the kidney. However, once your unborn child has been diagnosed with the condition, there are some things you’ll need to be aware of.
Pyelectasis isn’t usually visible until the second trimester. Because most cases are mild and do not cause observable discomfort or significant risk to the fetus, there aren’t any natural warning signs. Medical professionals would only detect the condition during a routine ultrasound.
The normal window for detection opens during the second trimester as the fetus’s kidneys have had enough time to develop by then. In short, imaging is the only way to receive a fetal pyelectasis diagnosis.
When it comes to mild cases of fetal pyelectasis, there are no perceptible symptoms with the fetus itself. You can rest assured that your unborn baby isn’t suffering in any way.
After your baby’s birth, the medical team will conduct an early ultrasound along with other investigations, such as blood tests looking at kidney function, blood pressure checks, and urine tests.
Prenatally diagnosed pelviectasis may indicate significant urinary tract issues that are proportional to the severity of the finding. As such, the two main causes of the condition are treated postnatally if necessary.⁹
Mild pyelectasis requires very little treatment because the condition usually goes away on its own. Your provider will likely monitor the situation throughout the remainder of your pregnancy with repeat ultrasounds.
For more severe cases, your provider will likely continue to monitor your newborn for some time.
Some babies with pyelectasis secondary to vesicoureteral reflux may be given prophylactic antibiotics. This is to prevent a urinary tract infection, as this is supported by some guidelines.¹⁰
Surgery may be needed to reverse blockages, but only in very rare and pronounced cases.¹¹
Pyelectasis of the fetus is a fairly common finding that can affect an unborn baby once their kidneys begin to develop. It’s usually due to a blockage of the ureter or vesicoureteral reflux (where urine flows in the opposite direction back into the kidney).
Although the condition sounds serious, most cases resolve spontaneously, remain stable, or improve after birth. Most cases are diagnosed during a routine ultrasound in the second trimester and will be monitored with repeat ultrasounds.¹²
As always, consult with your obstetrician or other healthcare provider if you have any questions or concerns regarding pyelectasis of the fetus.
No. It is a relatively common issue that occurs in developing fetuses.
While there is some correlation between the condition and Down syndrome, most pyelectasis cases are not associated with any genetic conditions and will resolve with time.
Pelviectasis is another name for pyelectasis, which is a pooling of urine in a developing fetus’ kidney. This occurs in the central part (pelvis) of the kidney specifically.
Over 90% of cases resolve on their own. Severe cases occur infrequently and would need a slightly higher level of medical intervention.
Yes, they are the same finding.
Pyelectasis is typically caused by either a blockage in the ureter or urine that flows backward into the kidney from the bladder.
No. Over 90% of all cases resolve on their own without medical intervention.
Time and medical supervision are all that’s necessary. No other interventions are required.
Kidneys | National Cancer Institute
Antenatal urinary tract dilation | The Royal Children’s Hospital Melbourne
Vesicoureteral Reflux (2008)