Pyelectasis And Down Syndrome

Introduction

Pyelectasis affects about 1% of all pregnancies, with people assigned male at birth (AMAB) being more susceptible rather than people assigned female at birth (AFAB). The collection of urine in the renal pelvis, the central region within the kidneys, causing the kidneys to grow larger than what is normal, is termed pyelectasis or pelviectasis. 

In an ultrasound, the detection of pyelectasis during pregnancy is regarded as a “soft marker”. Soft markers are certain specific sonographic features usually appearing during 16-22 weeks of a pregnancy.

These soft markers can potentially point towards any foetal chromosomal abnormality that could occur. Not all soft markers affect foetal health. However, possessing a soft marker implies that there is a slight increase in the chance that the baby might have a chromosomal anomaly, for example, Down Syndrome.

This article aims to provide a review of the current literature and research on the relationship between pyelectasis and Down syndrome. Further, we explore the potential genetic factors and underlying mechanisms that could contribute to this association. 

What is Down Syndrome?

Also referred to as Trisomy 21, Down syndrome is a condition in which an individual has an extra copy of a chromosome, specifically chromosome 21. A chromosome is a minute “package” of genes present in the body, normally present in pairs of two. The occurrence of an extra chromosome copy is medically referred to as a ‘trisomy’. This extra chromosome causes the foetal brain and body to develop in a different way, leading to both mental and physical challenges for the baby afflicted with this condition. 

A few common physical characteristics of Down Syndrome are:

• Small ears
• Almond-shaped eyes that tend to slant upwards
• Smaller feet and hands
• Presence of a palmar crease, a single line across the palm
• Looser joints or poorly toned muscles
• Smaller in stature
• Brushfield spots, i.e. Tiny white spots on the iris of the eye
• Short neck, with excess skin at the back of the neck
• Macroglossia, where the tongue is larger than normal
• Flattened face and nose 

Other cognitive issues, like:¹

• Impulsive behaviour
• Slow grasp
• Delay in language and speech development
• Short attention span
• Poor judgement

The cause and occurrence of this is still unknown, but the age at which the mother conceives has been the only commonly linked factor that tends to increase the chances of the foetus being born with Down Syndrome. The chromosome that causes Down Syndrome can be inherited from either parent. 

Soft biomarkers for pyelectasis and Down syndrome

Although the presence of pyelectasis serves as a soft biomarker for the prenatal detection of Down syndrome, further biomarkers could help in the detection of the likelihood of this syndrome occurring and the chromosomal abnormalities. Some other soft biomarkers associated with this are:²

• Foetal nasal bone hypoplasia: Absence of a nasal bone on the foetus by the second trimester of the pregnancy via examination of an ultrasound scan
• Parameters of growth in a foetus: Variations in normal foetus growth could be indicative of intrauterine growth restrictions in relation to chromosomal abnormalities. Decreased circumference of the abdomen or length of the femur are some of the growth characteristics that can be assessed using serial ultrasound measurements
• Nuchal translucency (NT) Thickness: Seen in the first trimester of pregnancy, an increase in nuchal translucency thickness points to an increase in the risk of the occurrence of chromosomal abnormalities. An NT measurement above the 95th percentile range should be followed with further diagnostic testing
• Hyperechoic bowel: An increase in echogenicity of foetal bowel in an ultrasound could be indicative of a gastrointestinal abnormality or meconium ileus - where the baby’s first bowel movements (meconium) tend to get stuck, leading to a blocked ileum

How is pyelectasis detected?

Foetal pyelectasis is identified through ultrasound scans and can be classified according to gestational age:

→ Between weeks 15 - 20: greater than or equal to 4 mm

→ Between weeks 20 - 30: greater than or equal to 5 mm

→ Between weeks 30 - 40: greater than or equal to 7 mm

Persistent foetal pyelectasis is characterised by dilation > 7 mm during the third trimester.³ 

Maternal hydration influences the foetus’ renal pelvic diameter. The urine production within the foetus is mediated partially by the amniotic fluid volume through maternal hydration.⁴ Progesterone levels also tend to influence the smooth muscles in the mother’s ureter and the foetus.⁵

Any alterations in renal function and development, thereby affecting genetic factors of the growing foetus can lead to the manifestation of pyelectasis in individuals. This onset of pyelectasis could then cause Down syndrome. 

Diagnostic techniques such as chorionic villus sampling or amniocentesis can be used to detect chromosomal abnormalities.

Clinical significance of pyelectasis and Down syndrome

In most cases, isolated pyelectasis - the occurrence of pyelectasis without any other co-morbidities in foetuses with Down syndrome tends to heal on its own shortly after birth or even at times, during pregnancy without causing any significant health issues.⁶

However, severe or prolonged pyelectasis can lead to further issues such as urinary tract infections (UTIs), impaired functions of the kidneys, or even kidney stones. Conditions such as vesicoureteral reflux and ureteropelvic junction obstruction (UPJO) can lead to pyelectasis. 

Amniotic fluid is made up partly of the foetus' urine, if there is trouble in urination, the amniotic fluid will also be scarce. The lack of amniotic fluid within the womb makes it harder for the foetal lungs to develop. This is because the foetus practises how to breathe, by breathing in the amniotic fluid in the womb. 

Hence, after birth, the baby will be watched for swelling in the kidneys (hydronephrosis), lung development, and scarcity of amniotic fluid. 

Treatment of pyelectasis

During pregnancy, regular ultrasound scans are conducted in order to judge and monitor the growing foetus’ health. Pyelectasis can be detected around weeks 16-22. 

Once detected, an ultrasound is conducted every 4 weeks to watch the foetus’ progression until it is born. The exact treatment depends on the extremity of the condition and the severity of the swelling. 

At times, with light swelling, can subside on its own and no further treatment is required. In cases where the condition leads to severe reflux or blockages, surgery can be used to revert this. 

In order to properly manage pyelectasis, once diagnosed, it is managed by a team of multidisciplinary professionals. A collaboration is required between maternal-foetal specialists, obstetricians, paediatricians, and genetic counsellors. 

Genetic testing should be carried out in order to assess the likelihood of the foetal pyelectasis leading to Down syndrome. Renal functioning should also be closely monitored and prenatal imaging can be recommended to assess the resolution and progression. 

FAQs

How often does pyelectasis mean Down syndrome?

More commonly observed in foetuses that have Down syndrome, in comparison to the general population. However, correlation does not lead to causation in this case, where the occurrence of pyelectasis alone does not definitively point toward the presence of Down syndrome. In numerous instances, pyelectasis tends to resolve itself without causing any chromosomal abnormalities. 

Can you tell the difference between a Down syndrome foetus and a normal foetus on an ultrasound?

No, ultrasound alone cannot definitively diagnose Down syndrome. Genetic testing, such as amniocentesis or chorionic villus sampling (CVS), is typically used to confirm a diagnosis of Down syndrome. 

Does fluid in the foetal kidney mean Down syndrome?

While pyelectasis may be more common in foetuses with Down syndrome, it does not exclusively indicate the presence of it. Pyelectasis can occur in foetuses without Down syndrome and may resolve on its own without causing any health issues.

What are the implications of pyelectasis in a foetus with Down syndrome?

The presence of pyelectasis in a foetus with Down syndrome could further lead to the progression of urinary tract infections or impairment of kidney functioning. 

Can pyelectasis in a foetus with Down syndrome be treated?

In many cases, mild to moderate pyelectasis resolves on its own without intervention. However, healthcare providers may recommend regular monitoring through prenatal ultrasound examinations to track the progression of the condition. In severe cases, or if other complications arise, medical or surgical interventions may be considered.

What is the long-term outlook for individuals with Down syndrome and pyelectasis?

The long-term outlook for individuals with Down syndrome and pyelectasis varies depending on the severity of the condition and any associated complications. With appropriate medical management and support, many individuals with Down syndrome and pyelectasis lead healthy and fulfilling lives.

Summary

Pyelectasis, the accumulation of urine within the kidneys, when found prenatally, is very closely associated with a high risk of developing Down syndrome. This is a subject that is still undergoing research and early detection followed by a comprehensive evaluation of it using soft biomarkers and ultrasound scans is recommended. Further studies need to be conducted to elucidate the mechanisms that underlie this condition and how it is linked to Down syndrome. As of now, the treatment is to watch the progression and consult with your healthcare provider on how to act on it depending on its progression.