Overview

Pregnancy involves a miraculous process filled with intricate biological steps, most of which go unnoticed until something goes wrong. One such disruption, Potter syndrome, occurs when the amniotic fluid – a protective cushion for the developing foetus – becomes dangerously low. This condition can lead to severe developmental abnormalities, making early detection and understanding essential. In this article, we will dive into the pathophysiology of Potter syndrome and its profound effects on foetal development.

What is amniotic fluid?

Amniotic fluid is a key part of pregnancy and is important in helping the foetus grow and stay healthy. It surrounds the foetus inside the amniotic sac and creates a clean, warm space that supports development and protects the foetus from outside harm. This fluid changes in both amount and composition throughout pregnancy, depending on the foetus, placenta, and the mother.^1,2

Role of amniotic fluid in pregnancy

• Amniotic fluid helps protect the baby by cushioning against injury and lowering the risk of infection due to its natural antibacterial properties
• Supports growth: it allows the foetus to move freely, which helps muscles and bones grow properly, and prevents the umbilical cord from getting squeezed
• Regulates the foetal environment: it helps control the foetus' body temperature and supports the development of the digestive system as the foetus swallows amniotic fluid
• Helps the lungs develop: amniotic fluid helps the air sacs (alveoli) expand through gentle pressure and provides proline, an important nutrient that helps the lungs mature
• Provides nutrients: it contains important substances like proteins, electrolytes, vitamins, and antibodies from the mother that help nourish the baby 
• Helps healthcare providers monitor the baby: doctors can study the fluid to check how the pregnancy is going and to get clues about the foetus's health^1,2

Production and elimination of amniotic fluid during pregnancy

Production of amniotic fluid

In the first two months, amniotic fluid comes from two main sources:^1,2

• The mother’s bloodstream: water and nutrients pass from her blood into the amniotic sac
• Special early pregnancy fluids: the ‘coelomic cavity’ (a temporary nutrient-rich sac) and the growing ‘amniotic cavity’ contribute fluid to protect the developing embryo

At this point in foetal growth, the fluid is thicker and acts like a feeding system for the embryo. 

After 8 weeks of pregnancy, the foetus begins to contribute more to the production of amniotic fluid, mainly through:

• Foetal urine: around 10 weeks of development, the foetus's kidneys start working, and their urine forms the majority of the amniotic fluid
• Lung secretions: fluid from the baby’s breathing movements makes up about a third of the amniotic fluid

At this stage, the amniotic fluid is primarily clear and has a watery consistency.^1,2

Elimination of amniotic fluid

• Swallowing: the foetus drinks amniotic fluid (starting as early as 11 weeks), which is then processed by the kidneys and excreted again via urination
• Intramembranous absorption: some fluid is absorbed directly into the foetus's bloodstream through the placenta and membranes^1,2

The elimination of amniotic fluid changes during pregnancy. In the first weeks of pregnancy (before 8 weeks), the foetal skin is thin, so fluid passes easily in and out. However, after 25 weeks, the skin thickens (keratinisation) and no longer absorbs fluid, so breathing, swallowing and urinating become the main ways to regulate fluid levels. A dynamic equilibrium of fluid secretion and resorption keeps amniotic fluid levels stable during pregnancy.^1,2

Understanding appropriate amniotic fluid volume during pregnancy

A healthy amount of amniotic fluid is usually an amniotic fluid index (AFI) of 5-25 cm, or a single deepest vertical pocket (SDVP) measuring 2-8 cm. However, fluid levels don’t stay the same. They change as pregnancy progresses. In early pregnancy, fluid increases steadily, peaking around 33 weeks. At 29-37 weeks, levels stay fairly stable. After 39 weeks, fluid drops quickly, and by 41 weeks, the average is about 515 ml (just over 2 cups).¹

Other factors that affect amniotic fluid levels include:¹

• First-time moms tend to have slightly lower fluid levels than women who have previously had babies
• Race and ethnicity may also play a role, especially after 35 weeks

Too little amniotic fluid (oligohydramnios), i.e. when the Amniotic Fluid Index (AFI) is equal to or less than 5 cm, or the SDVP measures less than 2 cm, may lead to the development of Potter syndrome.¹

What is Potter syndrome?

Potter syndrome, also known as Potter sequence, is a rare, severe, life-threatening congenital disorder that affects newborns because of oligohydramnios in the womb (uterus). Potter syndrome occurs in about 1 out of every 2000 to 5000 births. This syndrome shows a male predominance in occurrence rates. It most commonly affects first-time pregnancies in people aged 20 to 30 years.^3,4,5

Potter syndrome includes several types, each based on the cause. In classic Potter syndrome, both kidneys fail to form (bilateral renal agenesis), and this type is always fatal. 

• Type I cases, when autosomal recessive polycystic kidney disease, an inherited recessive disorder, is the underlying cause 
• Type II Potter syndrome results from kidney cysts and abnormal development (renal cystic dysplasia) 
• Type III Potter syndrome results from autosomal dominant polycystic kidney disease (ADPKD)
• Type IV develops when a long-term blockage in the kidneys or ureters prevents normal urine flow⁴

Pathophysiology of Potter syndrome

The most common cause is bilateral renal agenesis – both kidneys failing to develop. Without kidneys, the foetus cannot produce urine, essential for maintaining amniotic fluid.³

Other causes include:^1,3,4

• Premature rupture of membranes before labour
• Maternal health conditions: high blood pressure, diabetes, or use of medicines that lower blood pressure or reduce fluid production, such as ACE inhibitors, angiotensin receptor blockers (ARBs), indomethacin, use of cocaine or preeclampsia
• Foetal growth restriction (FGR) – the baby grows poorly due to placental problems, leading to reduced urine output
• Twin-to-Twin Transfusion Syndrome (TTTS): in identical twins, one baby (the donor) loses fluid to the other, causing low amniotic fluid
• Chromosomal abnormalities (e.g., Trisomy 18 or Trisomy21) can affect kidney development
• Genetic factors (gene mutations like PAX2 or HNF1B that affect kidney development)

Some cases are inherited through dominant or recessive genes, with the dominant being the most serious. Potter syndrome can also occur randomly, with no known family history.³ These conditions affect kidney function, leading to oligohydramnios.

Oligohydramnios effects on the foetus

Oligohydramnios (low amniotic fluid) leads to developmental abnormalities in Potter syndrome. These include the following abnormalities, explained by the limited space in the uterus (womb) due to low amniotic fluid restricts foetal movements, which directly affects muscle and bone development:⁴

Distinct facial features (Potter faces)

• Flattened nose
• Low-set ears
• Recessed chin
• Affected infants often have wide-set eyes and epicanthic folds (extra skin covering the inner eye corners)⁴ 

Limb abnormalities

• Club foot or hip dislocation (due to restricted movement in the womb)
• Extra fingers or toes (polydactyly)⁴ 

Underdeveloped lungs (pulmonary hypoplasia)

Oligohydramnios restricts foetal chest movement, leading to underdeveloped lungs (pulmonary hypoplasia). Without enough fluid, the foetus is compressed inside the uterus, and pressure from the belly organs pushes up on the diaphragm. This prevents the chest from expanding, maintaining the airways and alveoli collapsed. Also, amniotic fluid contains nutrients like proline, which help the lungs develop. Without it, lung growth is affected.^3. As a result, respiratory failure occurs shortly after birth.

Heart defects

Some infants also have heart defects, such as pulmonary valve atresia – a missing or closed valve that blocks blood flow to the lungs – occurring alongside Potter syndrome. The reason for this may be because they share the same genetic causes.⁵

Other abnormalities

Other possible abnormalities linked to Potter syndrome include: cysts in the pancreas, a blocked or missing oesophagus (esophageal atresia), defects in the duodenum, missing parts of the colon (colonic agenesis), a pouch-like structure in the intestine called a Meckel diverticulum, eye defects such as cataracts and lens displacement and bleeding. In rare cases, heart defects like ventricular septal defects, tetralogy of Fallot, and patent ductus arteriosus may also be present. Also, about seven out of ten people with this condition have deformed genitals.³

Although not every case of oligohydramnios will cause Potter syndrome, regular ultrasound scans to detect abnormalities and checks of amniotic fluid levels are important to help detect this condition early.⁴

FAQs

Can Potter syndrome be detected during pregnancy?

Yes, doctors can detect Potter syndrome before birth using routine ultrasound scans. These scans can show signs like missing or abnormal kidneys and low amniotic fluid levels. If ultrasound results are unclear, MRI scans provides clearer images.⁴

Is Potter syndrome always fatal?

Classic Potter syndrome, caused by the complete absence of both kidneys, is always fatal. The baby usually cannot survive due to severe lung underdevelopment. Other types may vary depending on the cause and how much kidney function remains.^3,4 

Can Potter syndrome be cured?

There is no cure for Potter syndrome. Most infants are stillborn or pass away within hours/days due to lung failure. Rare cases with partial kidney function may survive longer but require lifelong dialysis or kidney transplants. Supportive care (oxygen, ventilation) may be given, but outcomes remain poor.^3,4

Summary

Potter syndrome is a congenital disorder primarily caused by kidney defects in the foetus, leading to little or no urine production. This leads to oligohydramnios (low amniotic fluid), which impairs proper lung growth, causing pulmonary hypoplasia. The lack of fluid also causes physical compression, leading to typical facial features and limb deformities.