Overview

Did you know that fetal urine makes up most of the amniotic fluid in the second and third trimesters? If you are concerned about Potter syndrome or Multicystic dysplastic kidneys (MCDK) and their impact on amniotic fluid levels, or simply want to learn more, you are in the right place. 

Potter syndrome is a rare and fatal condition in fetal development where the physical appearance of the fetus changes due to oligohydramnios (low amniotic fluid during pregnancy), which we will get into later.¹ Multicystic dysplastic kidney is a disorder where one or both of a baby's kidneys don’t develop well, with cysts affecting their function.² 

Recognising the effects of these conditions on pregnancy and fetal health is important. Stick around as we’ll explore how these two conditions impact amniotic fluid.

What is amniotic fluid?

Amniotic fluid is a substance made up mostly of water and, later, babies' pee. Other molecules include lipids, hormones, antibodies, and nutrients. They are contained within a balloon-like structure until the ‘water breaks’ and fluid comes out.

While living in our mom's uterus, getting all the nutrients we need, amniotic fluid keeps us safe by acting as a pillow. Furthermore, it assists in the formation of the baby's digestive, respiratory and muscular systems. The fetus swallows the fluid, contributing to its maturation. 

The kidneys of a baby start developing around 16 weeks of pregnancy, and then begin producing urine. If there is something wrong with their development, the amniotic fluid levels drop. This state is known as oligohydramnios. 

On the other hand, a large-scale study involving 1200 pregnant women reported that larger fetal kidney volumes can lead to higher amniotic fluid levels.

What is Potter syndrome?

Potter syndrome is a condition occurring due to oligohydramnios during pregnancy.¹ The main cause is bilateral renal agenesis - a condition where both kidneys are missing. It sounds scary, and it is because this means a fetus can’t produce urine.

Other possible causes of Potter syndrome are polycystic kidneys and early rupture of membranes.

Consequences of Potter Syndrome

Lack of amniotic fluid makes the fetus look in a certain way, with flattened facial features, deformities of limbs, and underdeveloped lungs. These traits lead to complications and result in respiratory failure at birth. Together, this is known as the Potter sequence.

What is Multicystic Dysplastic Kidney (MCDK)?

MCDK is a disorder in which one or both kidneys don’t develop properly in the womb. The term ‘multicystic’ indicates that many cysts are formed, while ‘dysplastic’ refers to abnormal development. Consequences include deformed structure and functions of the kidneys.²

There is unilateral and bilateral MCDK. As you can guess, unilateral affects only one kidney, and the other kidney develops normally, taking on all of the functions. People with this condition can live normally without symptoms. Bilateral MCDK affects both kidneys, and it is more serious, leading to problems with urine production. In most cases, it ends up fatal. 

How does this affect levels of amniotic fluid?

Healthy kidneys are in charge of regulating fluid and electrolyte balance, supporting the development of lungs, and producing urine in the fetus. As we already mentioned, urine makes up most of the amniotic fluid in the second and third trimesters, so the consequences of these conditions are low fluid levels or complete absence of amniotic fluid (anhydramnios). Further on, this leads to deformities of limbs and face, lack of oxygen and nutrients, restricted movement, and complications with lung development.³

Diagnosis and detection

These conditions can be detected with prenatal ultrasounds in the second trimester. Doctors can see if there are abnormalities in kidney structure or if one of them is missing. Additionally, there is the Amniotic Fluid Index (AFI),⁴ which measures levels of amniotic fluid. If the index is low, it suggests something is wrong with urine production.

Additional prenatal tests include:

• Fetal MRI 
• Genetic testing - checking for chromosomal abnormalities
• Serial ultrasounds - checking progress over time

Management and treatment options

Once the diagnosis is confirmed, focus should be on monitoring and preparing for the outcome. The following methods are used for monitoring:

• Regular ultrasounds for checking the development of the kidney and fetal growth.
• Checking AFI levels
• Non-stress tests⁵ to analyse the fetus's condition

FAQs

Can a fetus live with one kidney?

Yes, it can. The kidney that is left will get larger because the other one is missing, but it can function normally. Regular doctor visits are required, especially during childhood, to make sure the remaining kidney is working properly. These babies grow up to be healthy children and can live full lives. It is advised for individuals with only one kidney to avoid contact sports, which might harm the kidney, but with good protection, that is also possible. There is a risk that patients with one kidney could develop high blood pressure or protein in the urine, but this depends on individual clinical and lifestyle variables.

Is Potter Syndrome genetic?

It is not inherited genetically, but it can have some genetic aspects, meaning it can happen because of some other condition that is inherited. These include:

• Autosomal Recessive Polycystic Kidney Disease - a genetic condition affecting the liver and kidneys where both parents carry a gene for it, but they are not aware of it because they are both healthy. There is a 25% chance (1 in 4) that the fetus will be affected
• Meckel-Gruber Syndrome - a genetic condition affecting the kidney and changes in the brain. It is also inherited in an autosomal recessive way, so same 25% chance of recurrence if both parents are carriers

Can amniotic fluid levels be increased?

Yes, they can, but it is most effective before the second and third trimesters because later urine makes up most of the amniotic fluid, so if there is an issue with the kidneys, the focus will be on monitoring. Ways to increase amniotic fluid levels include the following:

• Hydration - this makes sense, especially in cases of dehydration, and sometimes IV fluids are helpful as well
• Rest - having rest can improve blood flow, which could increase fluid levels
• Amnioinfusion (During Labour) - this is when sterile fluid is added into the amniotic sac through a tube placed in the womb

What support is available for families?

Parents are going through a lot in moments of finding out and then later on during monitoring, so it is advised to seek help in genetic or grief and trauma counselling. Other options are support groups, available online or in person, and various organisations dedicated to these causes. Education and practical resources are available to help parents navigate paperwork, as well as medical support from the staff.

Summary

Potter Syndrome and Multicystic Dysplastic Kidneys (MCDK) are conditions where the baby’s kidneys don’t develop properly, which can cause less amniotic fluid. Most of the amniotic fluid in the second and third trimesters is made from the baby’s urine, so if the kidneys aren't working correctly, there isn’t enough fluid. When kidneys don’t grow or function properly, fluid levels drop, causing developmental problems such as misshapen arms and legs, trouble with the baby's lungs not developing properly, and changes in how the baby’s face looks.

Potter Syndrome happens when a baby is born without kidneys, which stops urine from being made and can be very serious. Multicystic Dysplastic Kidneys (MCDK) is when the kidneys don't form properly and have cysts. If only one kidney is affected, the baby can live normally; however, if both kidneys are affected, it’s much more serious and can be fatal.

Doctors find these problems using ultrasound, tests to check the amniotic fluid, MRI scans, and genetic testing. While Potter Syndrome isn’t always inherited, it can be linked to conditions that run in families, like polycystic kidney disease or Meckel-Gruber syndrome.

Sometimes, doctors can increase amniotic fluid by encouraging hydration, rest, or, in certain cases, a procedure called amnioinfusion during labour. Families facing these challenges can find support through counselling, emotional help, and groups that provide useful resources.