What you need to know about ultrasounds

At some point in your pregnancy, your caregiver will probably suggest you have an ultrasound. Here's what to expect.

Photo: iStockphoto
Photo: iStockphoto

What is a prenatal ultrasound?
Also called a sonogram, this procedure uses soundwaves to create pictures of the baby (including the internal organs), placenta and amniotic sac. Most commonly, it’s done by gently rolling a device called a transducer over your belly.

Why have an ultrasound?
The Society of Obstetricians and Gynaecologists of Canada recommends that low-risk moms undergo at least one ultrasound during the second trimester, typically between 18 and 22 weeks. At this point, a sonogram can pinpoint the placenta’s location (if it’s covering the cervix, there’s a danger of bleeding), rule out the presence of an undiagnosed twin, and check for certain abnormalities. Various measurements taken during the test can also help confirm gestational age and establish a baseline that may be useful later on. For instance, if a question arises about whether the baby is growing well, a second (later) ultrasound can be done to check, explains Walter Romano, a radiologist and director of ultrasound at St. Joseph’s Health Care London (Ont.).

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More recently, some centres have also been offering an ultrasound between 11 and 14 weeks as one component of integrated prenatal screening (IPS). This involves using a measurement called nuchal translucency (the thickness of an area at the back of the neck), plus blood test results to gauge the risk of genetic abnormalities, such as Down syndrome. According to Rob Gratton, an associate professor of obstetrics and gynaecology at the Schulich School of Medicine & Dentistry, University of Western Ontario in London, IPS has a false positive rate of only one to three percent, versus eight percent for maternal serum screening, the older test for identifying such problems. (It’s important to note that IPS misses a small number of abnormalities, too.) Additional ultrasounds may be recommended if there are special concerns.

Is ultrasound mandatory?
Some women still opt to skip ultrasound because they’d rather be spared the anxiety and further testing an unclear result or a false positive poses, particularly if they’re certain they’d proceed with the pregnancy regardless. Another factor to consider is how convinced you are that the test improves outcomes for babies, since the evidence isn’t definitive one way or the other.

That said, many families not only find the experience reassuring, they’re tickled by the chance to sneak a first peek at their little peanut and capture a treasured photo for the baby book.

Keepsake ultrasound
Health Canada, the Society of Obstetricians and Gynaecologists of Canada and the Canadian Association of Radiologists all recommend that expectant parents not expose their unborn babies to ultrasound for the sake of making “keepsake” videos. For one thing, there’s a theoretical risk that prolonged exposure to high-frequency sound waves could damage tissue, and entertainment ultrasounds tend to last longer than the diagnostic variety. Plus, it’s possible the people operating the ultrasound machines may not be properly trained and certified.

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Originally published in March 2012. 

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