Diagnostic Ultrasounds Are ‘Incredibly Useful,’ Say Experts
The Technology Has Limitations, but No Confirmed Ill Effects

by Gayle Herbert Robinson

You’re 18 weeks pregnant and your doctor just ordered a full anatomical ultrasound examination. You’re excited and a little anxious. You can’t help but wonder if it will be safe for your baby. Physicians and sonographers resoundingly say yes.
“Expectant mothers can feel safe having ultrasounds because they do not involve ionizing radiation (x-rays) that can be harmful to growing fetuses,” says Richard L. Fischer, MD, co-division-head of Maternal-Fetal Medicine at Cooper University Hospital in Camden, NJ.
“It’s an incredibly useful tool,” says Beverly Coleman, MD, chief of Ultrasound at the Hospital of the University of Pennsylvania (HUP) in Philadelphia. “It’s the only one deemed safe for pregnant women to get evaluated. It supplies information when there is a serious abnormality.”
Alfred Kurtz, MD, an ultrasound specialist at Jefferson Medical College in Philadelphia, says that although ultrasounds are a good diagnostic tool, they don’t answer every question. He advises expectant mothers, “not to worry about having them, or hold back having them out of unproven fear.”

How Ultrasounds Work
Prenatal ultrasound imaging is a common diagnostic medical procedure that uses high-frequency sound waves to produce dynamic images (sonograms) of organs, tissues, or blood flow inside the fetus. Here’s what happens.
A trained sonographer, radiologist or obstetrician places a transducer — which converts electrical energy into ultrasound waves — on the expectant mother’s abdomen. The transducer sends a stream of high-frequency sound waves into the body, then detects their echoes as they bounce off internal structures. When these sound waves return, the transducer converts them into electrical impulses that are processed to form an image displayed on a computer monitor.
Explains Dr. Fischer, “The ultrasound signal travels through the body until it strikes an object of different acoustic density. Some of the sound is absorbed as heat, some continues to be transmitted forward, and some reflects back toward the transducer, which is ‘listening’ for the returning signal.” These signals last 1 millisecond, or one-thousandth of a second.
In some cases, the ultrasound transducer is placed inside the vagina, providing a closer look at the uterus and surrounding structures. This is useful to exclude an ectopic (tubal) pregnancy.
In an e-mail interview, Steven A. Dowshen, MD, chief medical editor for KidsHealth.org in Wilmington, DE, lists ultrasound uses: “Ultrasounds are a standard procedure used to: 1) diagnose a pregnancy, 2) determine multiple pregnancies, 3) verify the age of the fetus, 4) detect birth defects and fetal movement, 5) evaluate the position of the placenta and 6) monitor the fetal growth and heartbeat.”

Current Technology
Today’s standard ultrasounds use more shades of gray compared to those taken in the 1970s and 1980s, producing images with improved resolution. They also use real-time images — a series of still pictures taken many times per second, similar to a movie —- to show fetal movement, such as the heart beat.
Color Doppler ultrasound allows doctors to see the flow of blood within many vessels inside the fetal body, which helps determine the direction of blood (for detecting heart defects), speed of blood (to detect fetal anemia), and resistance within the blood vessels (seen with
fetal growth abnormalities and preeclampsia).
3D and 4D imaging, the latest advancement, allow doctors to see surface images, such as the face, and to manipulate images taken inside the baby to detect certain types of birth defects.
According to the American Institute of Ultrasound in Medicine (AIUM), the benefits of diagnostic ultrasound exceed any theoretical risks.

Physical Effects and Risks
“There have been isolated reports of low birth weight, delayed speech, dyslexia and left-handedness in infants exposed to ultrasound in utero, though these studies have not been confirmed and were performed prior to reducing the power output on most diagnostic ultrasound equipment,” says Dr. Fischer. “Ultrasound also produces heat, which at higher energies could cause cavitation (hole formation). However, there are no confirmed biological effects on babies, mothers or providers.”
Currently, obstetrical ultrasound equipment is required to have an output of less than 94 milliwatts/cm2, using the ALARA principle (As Low As Reasonably Achievable).
“Every time you do ultrasounds you slightly increase tissue heat,” says Kurtz. “Of all the types, the one that can cause potential heating is the pulse Doppler. Performed in low doses and in short exposure times, Doppler
ultrasounds are safe.” However, he warns against using it during the first trimester (first 12 weeks) unless clinically necessary.
At HUP, “we have an in-house physics department that regularly checks the ultrasound pulses. The equipment is routinely maintained,” says Dr. Coleman.

Accuracy and Limitations
“Obstetrical ultrasound is very useful for the detection of many fetal abnormalities,” says Dr. Fischer. “Neural tube defects (spina bifida) can be detected more than 90 percent of the time with skilled examiners.
“Cleft lip is another condition that is readily detectable by ultrasound. However, it cannot detect all fetal abnormalities. Ultrasound can miss as many as 50 percent of fetal heart defects. The most commonly missed abnormalities are holes in the heart. It cannot detect mental retardation or cerebral palsy. It cannot definitely diagnose chromosomal abnormalities.”
While today’s ultrasound technology has its limits, medical practitioners are convinced that it is safe when conducted by properly trained technicians under conditions that conform to FDA regulations. Ultrasound can provide early detection of problems — or, for most moms-to-be, early reassurance.

Gayle Herbert Robinson is a local freelance writer.