by Wood D

New Dimensions in Prenatal Ultrasound: 3D and 4D

IMAGE For years, physicians have relied on traditional ultrasound tests to learn how far along a woman is in her pregnancy, as well as the size, health, and position of the developing baby. Now, four-dimensional (4D) ultrasound lets women and doctors look at facial features and watch the growing baby move.

The Way Ultrasound Works

An ultrasound scanner (or transducer) sends sound waves through the body. These sound waves bounce back to the scanner and produce an image on a computer screen. Ultrasound is generally safe for the developing baby and mother. A technician applies a gel before placing and moving the transducer over the skin. The transducer may also be inserted into the vagina.
The conventional mode of ultrasound scanning is two-dimensional (2D). In other words, the image is made up of thin slices, and only one slice can be seen at a time. Although such an image is very informative to ultrasound professionals, to the average person, the picture may not look at all like a baby.
With 3D ultrasound, a volume of echoes is taken, stored digitally, and shaded to produce life-like images of the fetus. A 4D ultrasound takes the images produced by 3D ultrasound and adds the element of movement. Now, the life-like pictures can move and the activity of the fetus can be studied.
The ability to obtain clear images and activity will depend on the stage of pregnancy and the position of the fetus during the ultrasound exam.

Benefits of 3D/4D Ultrasound

3D and 4D ultrasounds can display activities of the fetus that are not possible with 2D. The fetus can viewed yawning, smiling, crying, swallowing, blinking, and moving fingers with 4D.
This may reveal more detail about fetal health and small movement. Just as a pediatrician begins an exam by observing a newborn, doctors assess the fetus from head to toe on screen. Watching him or her shift position and breathe, your doctor can check for problems.
Being able to view the developing child’s face may promote bonding. Women typically go home with a set of photographs and a CD with the moving images, which is why this ultrasound process is often called "keepsake fetal imaging." .

Cautions

As with other diagnostic imaging, 4D ultrasounds require a doctor’s order and a medical purpose. The American Institute of Ultrasound in Medicine (AIUM) and The American College of Obstetricians and Gynecology do not advocate the use of obstetric ultrasonography without a medical indication.
There is a strong consumer market for 4D ultrasound—even if it might pose as yet undiscovered risks. Because it has no proven benefit over 2D images, some insurance companies do not cover 4D imaging, even with a doctor's order. Despite theoretical risks and extra costs, some expectant parents may choose to obtain ultrasounds on their baby anyway. Most others choose the old fashioned way: waiting until the baby is born to see what he or she looks like.

RESOURCES

American Congress of Obstetricians and Gynecologists http://www.acog.org/

American Institute of Ultrasound in Medicine http://www.aium.org/

CANADIAN RESOURCES

Health Canada http://www.hc-sc.gc.ca/hl-vs/preg-gros

Women's Health Matters http://www.womenshealthmatters.ca/

References

ACOG committee on ethics. Nonmedical use of obstetric ultrasound. Obstet Gynecol. 2004;104(2):423-4.

Church CC, Miller MW. Quantification of risk from fetal exposure to diagnostic ultrasound. Prog Biophys Mol Biol. 2007;93:331-53.

Keepsake fetal imaging. American Institute of Ultrasound in Medicine website. Available at: http://www.aium.org/resources/statements.aspx. Approved April 1, 2012. Accessed July 22, 2012.

Prenatal ultrasound in pregnancy. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated May 10, 2012. Accessed July 22, 2012.

Prudent use in pregnancy. The Association for Medical Ultrasound website. Available at: http://www.aium.org/resources/statements.aspx. Approved April 1, 2012. Accessed July 22, 2012.

Ultrasound exams. The American College of Obstetrics and Gynecology website. Available at: http://www.acog.org/~/media/For%20Patients/faq025.pdf. Published August 2011. Accessed July 22, 2012.

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