Introduction

Unfamiliar terms like pyelectasis and vesicoureteral reflux (VUR) may show up during prenatal scans or early check-ups, which can be unsettling. But understanding what they mean for your child’s health can offer clarity and reassurance. Both conditions involve the urinary system and can be picked up in babies during pregnancy or after birth. Although they have differences in patterns of development and treatment, these two conditions can be closely linked - understanding this connection can help to support long-term kidney health. This article takes a closer look at what pyelectasis and VUR mean, relate to one another, and why early detection and monitoring are important for protecting your child’s kidney health.

What is pyelectasis?

Pyelectasis, also referred to as pelviectasis, is the enlargement of the baby’s renal pelvis during pregnancy. This is the central area of the kidney where urine collects before moving into the ureter, then the bladder, and draining out of the body through the urethra. The intricate structure of the kidneys is imperative for their function in the filtration of blood and removal of waste products as urine. The kidneys also play a significant role in maintaining the body’s water and electrolyte balance.

Pyelectasis is a spontaneous, relatively common finding seen in about 1-5% of all pregnancies, more often in babies assigned male at birth (AMAB) than those assigned female at birth (AFAB). The temporary dilation due to urine buildup and inability for urine to be drained out can affect one or both of the kidneys.

Causes

Although the condition has been linked to premature development of the baby’s urinary system as well as genetic factors, like being a marker for the development of Down syndrome, the cause can be unclear.¹ Pyelectasis may also result from structural abnormalities in the kidneys, or develop secondary to other conditions, mainly VUR and ureteropelvic junction obstruction (UPJO), but also urinary tract infections (UTI), nephritis, kidney stones, or certain medications that affect urine flow.^{2, 3}

Diagnosis

Pyelectasis often presents with no symptoms, and it is commonly detected in 20-week routine ultrasound scans that check the baby’s internal organ development. The condition is diagnosed when the renal pelvis measures 4mm or greater from front to back up to 27 weeks, and 7mm or greater after 27 weeks.² It is graded from mild to severe based on how dilated the baby’s kidney(s) are, and swelling is monitored through postnatal follow-up imaging scans.

Clinical significance

Pyelectasis is usually a harmless, benign condition that may not require treatment; rather, it is monitored by healthcare professionals to ensure normal foetal development.³ It is not typically linked to any serious underlying health issues and can resolve on its own either before birth or shortly after without necessarily requiring any treatment. Interestingly, kidney enlargement can come and go on its own during pregnancy. However, in some cases, pyelectasis could lead to complications that require medical intervention.

What is vesicoureteral reflux (VUR)?

VUR is a condition that is characterised by the abnormal backflow of urine in the kidneys, from the bladder up into the ureters and back towards the renal pelvis. This causes an increase in the internal pressure of the kidneys, leading to swelling and subsequently pyelectasis. VUR mostly occurs in newborn babies and young children who are born with it - about 1-2% of children are diagnosed with VUR, and it is more common in babies AFAB than those AMAB.⁴ 

Although VUR usually self-resolves as babies grow and develop, it may lead to further complications if it persists. Frequent or severe UTIs typically occur in those with VUR: about 30% of babies experiencing UTIs are also affected by VUR.⁵ UTIs occur due to the bladder not fully emptying itself of urine and bacteria entering the kidneys with backflow. This causes pain when urinating, frequent urination, smelly urine, stomach pain, and fever, though VUR may also be symptomless.

Causes and types                                                                                  

VUR is known to have two main causes, which correspond to the type of VUR babies present with. These types are:

• Primary VUR - this is the most common type. It is caused by the irregular or incomplete formation of the valves located between the ureter and bladder. When valves are unable to ensure one-way flow properly or do not close adequately, this causes a backflow of urine into the kidneys. As the baby’s organs grow and mature, valves may begin to function correctly
• Secondary VUR - this happens due to a blockage or narrowing at the junction of the bladder and urethra, often affecting both kidneys. This prevents the complete drainage of urine, allowing urine to flow back up the ureters into the kidney. This increases pressure and causes the kidneys to swell. Secondary VUR can also be caused by problems in the nerves that control bladder function, which can prevent urine release from the body

In some cases, VUR can be caused by genetic factors that can increase the chance of babies developing the condition. Up to 20% of children with VUR have a family history of the condition.⁴ About 30-50% of siblings or children of affected parents can inherit VUR due to the combination of genes that are passed down or any faults, known as mutations, that occur in these genes, affecting kidney structure or function.⁶

Diagnosis

VUR is diagnosed using a combination of tests, such as urine and blood tests, which check for infection and kidney function, as well as blood pressure checks and imaging scans. Ultrasound scans are key in detecting reflux, and specialised scans like the DMSA scan, VCUG, or radionuclide cystography are used to confirm a diagnosis, assess severity, track urine flow and check for kidney damage.

How are these conditions related?

As pyelectasis is often routinely picked up during pregnancy scans and usually resolves on its own, it does not always cause any further complications. However, in some babies, it can be an early sign of a deeper cause or underlying condition, such as VUR. While not all babies with pyelectasis will have VUR, some studies have shown a possible connection between the two, especially when kidney swelling persists after birth.

Risk factors

Certain risk factors may increase the chances of VUR in babies diagnosed with pyelectasis, such as gender, if one or both kidneys are affected, abnormalities in the urinary tract and genetics. 

• Gender: Although babies AMAB with bilateral pyelectasis, which affects both kidneys, can have a slightly higher risk of having underlying VUR, VUR is most commonly diagnosed in babies AFAB^{3, 4} 
• Urinary tract abnormalities, such as posterior urethral valves and ureterocele. These can increase the risk of VUR as they interfere with normal urine flow and restrict urine from exiting the bladder, causing urine reflux and kidney swelling.^{7, 8} In addition, babies with a family history of VUR and those with bladder and bowel dysfunction (BBD) can carry a higher risk of developing VUR.⁷ This is due to structural abnormalities in the urinary tract that are passed down in families with a history of VUR. In babies with BBD, the incomplete emptying of the bladder and constipation put extra pressure on the urinary system, creating an ideal environment for urine backflow⁷
• Genetics: studies have also shown that genetics plays a significant role in the development of VUR, especially mutations in the SPRY1 gene, which is crucial for the structural development of the kidneys. Errors in this gene have been shown to cause abnormal placement of ureters, which can subsequently increase the risk of urine reflux

When should further investigation take place?

Doctors typically carry out further investigations if kidney dilation doesn’t resolve after birth, if it worsens over time, or if the baby develops a UTI. In these cases, additional imaging or follow-up tests may be used to check for underlying reflux and ensure proper kidney drainage.

Long-term effects on kidney health

With routine monitoring, most babies with mild types of pyelectasis and VUR  outgrow the condition without any lasting health issues. However, when urine reflux is more severe or leads to frequent UTIs, it can strain the kidneys and present a risk of further complications.

Over time, the constant kidney swelling in pyelectasis and backflow of urine in VUR can cause permanent damage to kidney tissues, known as renal scarring.⁹ In some cases, this can raise blood pressure later in life or can contribute to long-term kidney problems, including kidney failure.⁹

This is precisely why early diagnosis, regular monitoring, and correct management of pyelectasis and VUR are key to protecting your baby’s long-term kidney health.

Monitoring and treatment

In many cases, both pyelectasis and low-grade VUR resolve on their own, so a ‘wait and watch’ approach with regular imaging scans is often used to keep the conditions under control.³ In babies with VUR, preventing UTIs through adequate hydration, encouraging frequent bladder emptying and regularly changing diapers can help prevent bacterial spread and further complications.

Daily low-dose antibiotics may be prescribed to prevent infections, especially in severe cases and for frequent UTIs.⁴ Doctors may also prescribe ACE inhibitors to help protect the kidneys due to high blood pressure. Babies with persistent reflux may be referred for surgical options to resolve faulty kidney valves and enable them to close properly.

Pyelectasis doesn’t require treatment, and regular follow-up scans, in addition to urine and kidney function tests, are used to monitor the kidneys. However, if pyelectasis is linked to an underlying condition like VUR, then it is crucial to treat the root cause of VUR.2, 3 Early Management of the symptoms and a tailored treatment plan are key in preventing complications.

Summary

Pyelectasis, also referred to as pelviectasis, is the enlargement of the baby’s renal pelvis during pregnancy. VUR is a condition that is characterised by the abnormal backflow of urine in the kidneys, from the bladder up into the ureters and back towards the renal pelvis. This causes an increase in the internal pressure of the kidneys. Though often harmless on their own, pyelectasis and VUR can affect kidney health if they are not monitored closely and left untreated. VUR can be the underlying cause in many cases of pyelectasis, so early detection and management are imperative in protecting long-term kidney health, as is understanding how these two conditions are connected. With regular follow-ups, proper clinical investigation, early diagnosis and appropriate treatment, further complications can be prevented and your child can go on to live a full and healthy life.