This leaflet is to help you understand what Fetal Polycystic Kidneys are, what tests you need, and the implication of being diagnosed for you, your baby, and your family.

What are fetal polycystic kidneys?

Polycystic kidneys are a rare abnormality that can affect the baby in the uterus. In this specific genetic condition, the fetal kidneys are enlarged and appear very bright in ultrasound due to the presence of numerous small fluid-filled cysts. The kidney function is usually abnormal, with gradual onset of impairment of kidney function. Usually, both kidneys are affected, thus the prognosis is guarded. 

There are two types of the disease with different modes of inheritance, the dominant and the recessive type. Based on the time of the disease onset there are different forms, namely prenatal, neonatal, infantile, and juvenile form.

How do polycystic kidneys happen?

The dominant type of polycystic kidney happens in about 1 in 20,000 babies, while the recessive type of the disease is in about 1 in 1000 babies. It is caused by a genetic abnormality (faulty gene). That means that there is an error in the message of the DNA in the cells. Each message of the DNA is called a gene. Each of us inherits our genes from our parents. They provide our bodies with instructions that influence our looks, health, and behaviour. In general, each person has two copies of every gene. One copy is inherited from the mother and the other from the father. 

Polycystic Kidneys occur due to a mistake (called a mutation) of the gene known as PKHD1. This gene is responsible for the production of a protein called fibrocystin or polyductin, which is believed to be involved in the formation and maintenance of the tubular structures in the kidney ducts. In the dominant type, one defective copy of the gene is enough for the manifestation of the disease, while in the recessive type both parents have to be carriers of a defective copy of the gene and when pregnancy occurs there is a chance 1 out of 4 that the baby will inherit both defective genes and will have the disease.

Should I have more tests done?

Polycystic Kidneys can be diagnosed before birth by testing DNA taken from the baby. This can be obtained by an invasive procedure called amniocentesis after the 15th week of pregnancy (or chorionic villus sampling - CVS between the 11th and 14th week of pregnancy). Applying these methods we collect cells from the amniotic fluid around the baby or from the placenta and we examine the DNA inside them. These methods are used for high-risk pregnancies, such as previously affected babies. Genetic testing (a blood test) must be done on the parents as well.

What are the things to watch for during pregnancy?

Polycystic Kidneys can also be suspected through ultrasound in pregnancy. However, the sonographic features are not always clear, thus, the diagnosis has to be confirmed via DNA examination or/and evaluation after birth. As the kidney function becomes abnormal, the fluid around the baby, which represents the fetal urine, is gradually reduced and the fetal bladder becomes non-visible with ultrasound. The condition is called oligohydramnios and is mainly seen in the recessive type of the disease. 

Short-term prognosis mainly depends on amniotic fluid volume and severe oligohydramnios have an extremely poor prognosis due to underdevelopment of the lungs and kidney failure. Cases with normal amniotic fluid volume will progress to kidney disease later on, usually before adulthood. It is also possible that the baby might die in the uterus and before birth. In the dominant type of the disease the prognosis is more favourable.

What does it mean for my baby after it is born?

The short-term prognosis mainly depends on amniotic fluid volume. Fetuses affected with the prenatal recessive type associated with severe lack of amniotic fluid (oligohydramnios) have an extremely poor prognosis due to underdevelopment of the lungs and kidney failure. Cases with normal amniotic fluid volume will later progress to an end-stage renal disease requiring kidney transplantation, usually before adulthood. They might also manifest complications related to liver fibrosis and require combined liver-kidney transplantation. 

Currently, no prenatal treatment exists and pregnancy termination is an option. Concerning the dominant type of the disease, the prognosis is more favourable. Complications in childhood include hypertension and protein in the urine, and patients may require renal replacement therapy (dialysis) at some point during their adult life. Early diagnosis and treatment with novel therapies might delay the onset of renal failure and hypertension-related complications.

Will it happen again?

In the recessive type, since the underlying cause is a recessive faulty gene, there is a 25% risk of recurrence (1 out of 4 cases). In the dominant type, since the underlying cause is a dominant faulty gene, there is a 50% risk of recurrence (1 out of 2 cases). This can be detected early in the next pregnancy with an invasive procedure.

What other questions should I ask?

  • Does this look like a severe case of polycystic kidneys?
  • Are there extra signs apart from the affected kidneys?
  • Is there a way to be sure of the diagnosis?
  • How should the pregnancy be followed-up?
  • Is there a treatment available during the pregnancy?
  • Where and when should I deliver?
  • What care will the baby receive after it is born?
  • Can I meet the genetic specialist?
  • Can I meet the kidney specialist?
  • Can I meet the team of doctors that will be assisting my baby when it is born in advance?

Last updated November 2022