Causes of antenatal hydronephrosis
Most cases antenatal hydronephrosis are not inherited and are not caused by anything that the mother does during her pregnancy.
Doctors think antenatal hydronephrosis that occurs without any other problems happens as the baby’s urinary system develops – especially if one or both ureters do not fully develop before the kidneys start making urine.
Occasionally, antenatal hydronephrosis is caused by other problems affecting the development of the kidneys or the urinary system. These include:
Vesico-ureteral reflux (VUR)
This occurs when some urine refluxes (goes back up) towards one or both kidneys. In severe VUR, the reflux reaches into the kidney, causing the antenatal hydronephrosis.
Blockage
Some cases of antenatal hydronephrosis are caused by a blockage (or obstruction) that partially or fully stops the flow of urine out of the kidney. If this is suspected, you may be referred to a paediatric urologist (a surgeon who treats children with problems of the urinary system).
There are different types of problems that cause a blockage. These may be diagnosed after a baby is born and may need treatment.
- Posterior urethral valves (PUV): some boys are born with extra flaps of tissue in part of the urethra, the tube that carries urine out of the body. After birth, a long, thin tube (catheter) is inserted into the urethra to drain urine. PUV are removed by surgery.
- Pelviureteric junction (PUJ) dysfunction (or PUJ obstruction): a blockage or narrowing between the renal pelvis (in the kidney) and the ureter, the tube that carries urine from the kidney to the bladder. In some cases, surgery is needed.
- Vesicoureteric junction (VUJ) dysfunction (or VUJ obstruction): a blockage or restriction to the flow of urine between the ureter and the bladder. Many cases get better on their own, but in some cases, surgery is needed.
- Duplex kidney: sometimes a kidney and ureter on one side of the body develop in two parts. In some cases, one of the ureters dilates (swells) where it goes into the bladder – this is called a ureterocele. In many cases, this will not need follow-up or treatment, but if it is associated with blockage or reflux, children may need more tests and occasionally surgery.
Sometimes, your doctor will not know why your baby has antenatal hydronephrosis and whether it will lead to problems later in the pregnancy or after birth. You may need more scans during the rest of your pregnancy to check whether the problem is changing. Your baby may need tests after birth to find out the cause and whether treatment is needed.
Will antenatal hydronephrosis affect other family members?
Antenatal hydronephrosis itself does not usually run in families, and it is not likely to happen in future pregnancies. A few conditions that cause antenatal hydronephrosis, such as VUR, may run in families and may be inherited from the mother or father.