Being pregnant


Everything you need to know about ultrasound

By Rhea Seymour


What is ultrasound?
Ultrasound is sonography, which uses high-frequency sound waves to allow visualization of the internal organs of the body. Computers translate the data from the sound waves into pictures. During pregnancy, it provides a view of the embryo or fetus.

How is an ultrasound performed?
During the painless procedure, which typically lasts between 30 and 45 minutes, a technician or radiologist will cover your bare abdomen with gel, which improves sound conduction, and then slowly move a transducer (a receiver that records sound waves and transfers the data to a computer to generate an image) across it. During the first trimester, the ultrasound may be performed by inserting a probe into the vagina to allow for a better view of the tiny embryo.

Why is ultrasound used during pregnancy?
According to Dr. Walter Romano, director of ultrasound at St. Joseph’s Healthcare in London, Ont., ultrasound is used to:

• determine gestational age;
• investigate any risks of miscarriage, such as pain or bleeding, or concerns that the fetus is under duress or not growing properly;
• detect subtle abnormalities in fetal organs and genetic markers for chromosomal abnormalities, such as Down syndrome;
• locate the fetus before the needle is inserted during amniocentisis, a procedure involving removal of the amniotic fluid from the sac of the developing fetus to evaluate for inherited genetic diseases, spinal defects and chromosomal abnormalities;
• examine fetal organs;
• confirm the baby’s position — for example, if a breech (feet or buttocks first) presentation is suspected — before delivery;
• confirm twin or multiple babies.

Ultrasound is also about 90 percent accurate in determining the gender of the fetus.

When can ultrasound detect abnormalities in the baby?
During the first trimester, ultrasound is being used more frequently in prenatal genetic screening. It enables the technician to measure the nuchal translucency — the skin on the back of the baby’s neck. “When correlated with the mother’s blood work, these measurements are a fairly accurate predictor of chromosomal abnormalities, such as Down syndrome,” says Romano.

Between 18 and 20 weeks, ultrasound allows for the examination of limbs, spine, heart, stomach, bladder and brain.

If my ultrasound results are good, is that a guarantee that my baby will be healthy?
“We’d like to think ultrasound is pretty accurate,” says Romano. “But even if you have a normal ultrasound at 18 weeks, it’s by no means a certificate that the fetus has no abnormalities. It’s a very good indicator that the fetus is normal, but there are false negatives — for example, the heart may look fine during the ultrasound and it turns out the baby has a congenital heart abnormality.”

Are there any risk factors?
After 30 years of widespread use of obstetrical ultrasound, ultrasound has no known risks, according to Romano. However, because it may yield false positives, it can create heartache for families. “Ultrasound may raise concerns about the fetus and in the end everything will be fine. For example, technicians look for soft markers for Down syndrome. If the fetus has the marker, it doesn’t mean it will have Down’s, but now we have the family concerned that the baby has it.”

This article was originally published on Apr 19, 2005

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