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Hydronephrosis (also known as pyelectasis or pelviectasis) is the presence of extra fluid in a fetus's kidney(s).

It is found in approximately 1-3 percent of ultrasounds done during pregnancy.

Causes of hydronephrosis

  • In some cases, hydronephrosis may be due to a blockage along the baby's urinary tract, making urine back up into his or her kidneys. Most of the time, this does not cause problems after birth; however, a small percentage of these babies require surgery after birth.
  • In most cases, there are no other abnormalities. However, hydronephrosis can be seen more commonly in babies with Down syndrome. The risk of Down syndrome is thought to be low when there are no additional risk factors, such as abnormal ultrasound or maternal serum screening results).

Further testing

  • You can have a more detailed ultrasound to look for other abnormalities. More ultrasounds may be recommended to monitor the size of the baby's kidneys and your amniotic fluid level. In some cases, we may recommend an evaulation by a pediatric urologist after birth.
  • The maternal serum screening can assess your risk of having a baby with Down syndrome, usually done between 15 and 20 weeks.
  • An amniocentesis can diagnose a chromosome abnormality. Amniocentesis involves obtaining a sample of thefluid surrounding the baby, which is then used to study the fetal chromosomes. There is a small risk of miscarriage from amniocentesis.
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