The term antenatal hydronephrosis is derived from the Greek words antenatal, meaning before birth, and hydronephrosis, meaning fluid in the kidney.
This condition is characterized by fluid filling the kidneys which causes enlargement of both the kidneys and the kidney's collecting system. Antenatal hydronephrosis is diagnosed by prenatal ultrasound studies and can be detected as early as the first trimester of pregnancy. In most cases, this diagnosis will not change obstetric care, but will require surveillance throughout pregnancy as well as after delivery.
Usual causes of antenatal hydronephrosis
- Obstruction: A blockage along the ureter may cause hydronephrosis. The most common site for blockage in the upper urinary tract is at the ureteropelvic junction (UPJ) or at the ureterovesical junction (UVJ). A blockage along the urethra in the lower urinary tract is usually due to posterior uretheral valves, and is only seen in boys. Significant obstructions may require surgical correction.
- Vesicoureteral reflux (VUR): Occurs when the "valve" between the bladder and ureter does not function correctly. This causes urine to flow backwards into the kidneys as the bladder fills and empties. About 75% of children will outgrow VUR as they get older, but they will require regular follow up and daily low-dose antibiotics until the condition resolves to prevent kidney damage. Surgical correction may be needed if a child does not outgrow the reflux or if they experience urinary tract infections while on antibiotics (also called "breakthrough infections").
- Duplication: Normally, each kidney has only one collecting tube system attached to it. However, 1% of children are born with 2 collecting systems from a kidney. Children with duplications are at a higher risk for other urinary problems, such as vesicoureteral reflux and ureteroceles (balloon-like obstruction at the end of one of the tubes). Testing may need to be done to rule out these other potential conditions.
- Multicystic Dysplastic Kidney: A multicystic kidney is a non-functional kidney that is actually a group of cysts. With the widespread use of prenatal ultrasound, the majority of multicystic kidneys are being detected before birth. Multicystic kidneys are almost always unilateral (affecting one kidney). Bilateral multicystic kidney (affecting both kidneys) is incompatible with life.
- "Normal" Variant: Sometimes hydronephrosis resolves before birth or it is very mild and does not cause any further health issues.
Management During Pregnancy
Your obstetrician will determine the most appropriate treatment plan for the rest of your pregnancy. In nearly all instances of antenatal hydronephrosis, ultrasound surveillance throughout the pregnancy is all that is necessary, and the labor and delivery process is generally routine.
Management After Birth
Postnatal ultrasound is usually performed after the first few days of life. If hydronephrosis persists, reflux and obstruction must be considered as possible causes and can be ruled out through diagnostic tests such as a voiding cystouretrogram (VCUG), intravenous pyelogram (IVP), or a renal scan. Some tests will be performed immediately and others may be delayed until one to two months of age to increase testing accuracy.