Ask The Doctor: Level 2 Ultra... Health Article

Jeffrey Ecker, M.D. is an Associate Professor of obstetrics, gynecology and reproductive biology at Harvard Medical School and a member of the Department of Obstetrics and Gynecology at Massachusetts General Hospital, where he practices maternal-fetal medicine.

Question:

My Ob/Gyn said they found fluid in the baby's kidneys during my 20-week ultrasound, so I have to have a level 2 ultrasound done. What does this mean?

Answer:

The significance of fluid in a baby's kidneys, like so many other things, depends on how much is seen, what happens over time, and whether everything else seems right on the ultrasound and testing. I suspect that the level two ultrasound (a scan designed to look at the developing organs and structures in great detail) has been ordered to help answer some of these questions.

Kidneys produce urine that runs through tube-like structures — the ureters — to the baby's bladder. From the bladder, urine flows out through the urethra to make the amniotic fluid that bathes the baby while inside the womb. On occasion there can be an obstruction along this path from kidney to amniotic sac. This is more common in boy as opposed to girl fetuses.

Obstruction may be the result of one of the tubes or paths not quite forming properly or kinking as it travels along its course. If the obstruction persists and even grows as pregnancy progresses, surgical correction may be needed after birth. Rarely, obstruction is enough to cause damage to one kidney, but this is very unusual, and as long as the other kidney seems healthy doctors will generally not recommend an early delivery simply to treat a one-sided obstruction. Repeat ultrasounds may be ordered to follow any progression of obstruction and fluid collection.

Sometimes fluid in the kidneys can be found absent any obstruction or kidney problem. Indeed, a small amount of fluid in the kidneys may be a very normal finding.

Some studies suggest, however, that babies in whom a small amount of extra kidney fluid is seen are at slightly increased risk for Down syndrome. Importantly, finding such fluid does not mean that your baby has Down syndrome. There are other tests that are much more predictive of Down syndrome. Your doctor will evaluate your risk in the context of your age and other tests you may have had, and help you decide if further testing such as amniocentesis is right for you. In most pregnancies, the finding of fluid in the kidneys alone will not lead couples to choose amniocentesis.