Introduction

Prenatal pyelectasis, commonly referred to as foetal pyelectasis, is the enlargement of the centre area of the kidneys, the renal pelvis, in unborn babies.¹ They may be found in routine ultrasound scans during pregnancy, particularly in the 20-week anomaly scan, when different conditions are checked by healthcare professionals.² Usually, prenatal pyelectasis is transient and can resolve on its own during the pregnancy or after the baby has been born.^2,3 In a minority of cases, it may be more severe and is linked to urinary tract abnormalities or infections, and Down’s syndrome.^2,4 Therefore, it is important for continual follow-up to decide if other tests and scans are needed and to detect if complications are present.

What is pyelectasis?

Structure and function of the kidneys

Kidneys are the vital organs in your body that filter excess fluid and waste from your blood, which is then passed out of the body as urine.⁵ From the renal artery to smaller branches of blood vessels, blood flows into the kidneys and reaches filtering units called nephrons. Water, minerals and other substances return to the blood, whilst anything that is in excess or is waste will be removed.⁵ In the middle of the kidneys, there is a hollow area called the renal pelvis. This is where the filtered urine funnels and flows into the ureter, which connects the kidneys and bladder.⁶

Prenatal pyelectasis

In pyelonephritis, there is an enlargement (dilatation) of the renal pelvis in one or both kidneys (unilateral or bilateral).¹ This can happen to people of any age and in unborn babies during pregnancy, more commonly in male babies.^1,3 Babies will continue to grow throughout the pregnancy, but when the kidneys are larger than 4-6mm in the second trimester or 7-10mm in the third trimester, it is classed as prenatal pyelectasis.^7,8 This is commonly seen in around 1-5% of pregnancies, and it may also happen to only one or both of their kidneys.¹ The exact causes of prenatal pyelectasis are not known, but there may be some links to other medical complications, such as blockages that affect the normal exit for urine or the backflow of urine.^2,3,9 There is also a low risk of Down’s syndrome, a genetic disorder.¹⁰ However, most cases are not a cause for concern, and some may even resolve on their own without intervention before birth or shortly after birth.² Therefore, it is important to be aware during pregnancy and regularly check up on it if discovered.

How is pyelectasis detected?

At 20 weeks of your pregnancy, the option of having an anomaly ultrasound scan will be provided to look for potential conditions the baby might have.¹¹ At this check-up, an ultrasound probe and some cold jelly will be placed on the skin.¹¹ The probe produces sound waves into the body, which will then bounce back, and that information will be collected and displayed on the computer.¹¹ The sonographer will look closely at the baby’s vital organs, bones, and the spinal cord, as well as check your blood flow and uterus.¹¹ A typical scan usually takes around 30 minutes in a dark room where the sonographer looks at the scans in real time.11 This may take longer if the baby is moving around or if it is difficult to take clear pictures of the baby. Occasionally, different healthcare professionals will also check the scans.

The normal range for the renal pelvis in the baby before 28 weeks is around 0-7mm, less than 8mm after 28 weeks, and less than 10mm after 32 weeks.¹² If, during the scan at 20 weeks, the renal pelvis looks larger than usual, the sonographer will measure the diameter. When the size is greater than 5mm, an ultrasound scan will be scheduled at 34 weeks.^2,12 If the renal pelvic diameter is bigger than 10mm, a referral to the foetal medicine unit will be made. Sometimes the ultrasound scan may not give a conclusive diagnosis, or more information is needed, then Magnetic Resonance Imaging (MRI) is used to see if the baby has pyelectasis.¹ MRI uses magnets and radio waves to produce detailed images inside the body, taking around 20-40 minutes.¹³ An MRI scan is not painful, nor does it use harmful radiation, so it does not pose any proven risks to you or the baby.¹³

The significance of prenatal pyelectasis

It may be concerning to learn about possible abnormalities or diseases your baby may experience. However, in many cases of prenatal pyelectasis, the enlargements may resolve by themselves as some will fall within the normal range over the course of the pregnancy, and some are due to normal genetic variation.^2,12 However, if the pyelectasis persists and becomes more severe, it may be linked to other health complications.

Possible outcomes

The enlargement of the renal pelvis may continue to increase to larger than 10mm and then is classified as foetal hydronephrosis, which also includes the dilatation of the calyces in the kidneys.^1,14 A more severe increase in size is linked to having a worse outcome, so follow-up is essential.¹⁵ If pyelectasis is caused by an obstruction or reflux in the urinary tract, surgeries may be needed to correct and preserve renal function.⁹ Prenatal hydronephrosis has been linked to a higher risk of urinary tract infection in the first few years of life.¹⁶ Though this is only a small portion of those diagnosed with prenatal pyelectasis.

There has also been a link between prenatal pyelectasis and Down’s syndrome, a genetic disorder.⁴ It is caused by an extra chromosome, and the disorder is commonly marked as trisomy 21.^17,18 If a child has Down’s syndrome, they will have some levels of learning disability, but their independence and care requirements will vary.¹⁸ The likelihood of having a baby with Down’s syndrome heightens as you get older.¹⁸

What happens after diagnosis?

Follow-up evaluations

When prenatal pyelectasis is detected in the second trimester, there will be a follow-up scan in the third trimester to see if the renal pelvis has continued to enlarge.^2,12 If the diameter is greater than 10mm, you will be seen by a doctor in foetal medicine to explain the significance of the scans, especially if there are any additional findings in the baby’s urinary tract.² You will also be able to speak to a doctor who works in the paediatric urology department to explain what will happen after the baby is born.¹² If, along with other tests during your pregnancy, it highlights a chance of your baby having Down’s syndrome, you can speak to a GP or be referred to a genetic counsellor to have a better understanding.¹⁸

Post-birth management

After your baby is born, routine kidney ultrasound scans will be scheduled in the first few weeks of life.² The doctor will prescribe antibiotics to minimise the likelihood of the development of urinary tract infections.² Continual check-ups will be made to see if the antibiotics are still needed once the course has finished, or if other treatment options should be considered.² In rarer cases, surgical procedures may be needed if pyelectasis is severe and is caused by an issue in the urinary tract, such as a blockage or reflux.⁹

Future pregnancies

If you are planning on having more children in the future, or if your baby had pyelectasis in your last pregnancy, there is a higher risk of pyelectasis recurring in your next pregnancy.^2,19 You will go through the same routine ultrasound screening to check if your baby has any abnormalities.²

FAQs

What is hydronephrosis, and is it the same as pyelectasis?

Hydronephrosis and pyelectasis have overlaps, but the main differences are that pyelectasis is less severe and only involves the renal pelvis, whereas the calyces are also enlarged in hydronephrosis.¹⁴

When should parents be concerned? 

Parents should feel reassured that most cases are mild and will resolve on their own.^2,12 When the condition continues and worsens, healthcare professionals will guide diagnosis with more tests and follow-up. If there are other abnormalities found or if kidney function is affected, specialist doctors and counsellors will provide more information for any questions that you may have.

Summary

Prenatal pyelectasis is usually a mild complication during pregnancy. It is normally detected through routine prenatal ultrasound, along with other disorders. This enlargement commonly resolves on its own, but rest assured, healthcare professionals will carefully manage and order more follow-ups and tests to ensure the health of your and the baby. Being able to detect complications early is vital to providing the best plan of care and treatment during and after the pregnancy. You will be referred to for counselling for urinary tract or genetic disorders, so that you can have the best understanding of the medical significance, as you wish.