Renal agenesis is a rare condition in which babies are missing one or both kidneys at birth. In this disorder, one or both kidneys fail to develop between the fourth and sixth week of gestation. There are two types of renal agenesis:
Bilateral renal agenesis
Bilateral renal agenesis, also known as Potter syndrome, means that both kidneys are missing. This occurs in about one in every 3,000 to 4,500 live births and is more common in boys. When neither kidney develops, it causes a lack of amniotic fluid, which is usually the reason for diagnosis as the low fluid levels are visible during a routine prenatal ultrasound.
Babies with no kidneys are unable to survive without treatment and the available treatments are still experimental. With no kidneys, the baby doesn’t produce urine, leading to low amniotic fluid and incomplete lung development.
Unilateral renal agenesis
Unilateral renal agenesis means that a baby develops only one kidney. Found in roughly one in 1,000 live births (higher in twins), this condition is not fatal and often causes no additional symptoms. When a baby has just one kidney, the organ grows larger to compensate and perform the functions of both.
Most babies born with one kidney live normal lives, but this condition is associated with abnormal development of the genitals in 12% of males and 40% of females.
What causes renal agenesis?
While the exact cause is unknown, unilateral renal agenesis is more common with intrauterine growth restriction (poor growth during pregnancy) and in multiples (twins, triplets, etc.). Unilateral renal agenesis is sometimes seen an association with a two-vessel umbilical cord, rather than the normal three-vessel cord.
The cause of bilateral renal agenesis, the absence of both kidneys, is also unknown. In most cases, there is no family history of the condition, though in around one-quarter of cases, there is a genetic component.
The risk of a future pregnancy being affected by renal agenesis is approximately 3 to 4%. If the renal agenesis is part of a condition with multiple abnormalities, the chance for it to reoccur in a future pregnancy may be as high as 8%.
How is renal agenesis diagnosed?
Both types of renal agenesis can be identified in sonographic findings. Unilateral renal agenesis is found when the one developed kidney is larger than normal for the gestational age. Hypertension can also develop due to this anomaly, leading to diagnosis and requiring postnatal follow-up examinations.
Bilateral renal agenesis can be observed through sonographic findings that detail complete or severe depletion of amniotic fluid levels at 14 to 16 weeks. The inability to visualize the fetal bladder after 16 weeks of pregnancy should prompt further investigation for bilateral renal agenesis.
As a parent, receiving the news that your child may be missing both kidneys can be devastating. Even a diagnosis of unilateral renal agenesis can be worrisome, but the Colorado Fetal Care Center is a national leader in diagnosing and treating both types of renal agenesis.