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Dr. Chew Answers: What is ultrasound imaging?

For more than 40 years, ultrasound imaging has been established as a safe and invaluable tool in the evaluation of the fetus. However, the long-term effects of repeated ultrasound exposures on the fetus are not fully known.

What is ultrasound imaging?

Ultrasound imaging is a common medical diagnostic tool that uses high-frequency sound waves to produce images (sonograms) of organs, tissues, or blood flow inside the body. Antenatal ultrasound examinations are commonly performed by sonographers, radiologists, and obstetricians. The procedure involves using a transducer, which sends a stream of high-frequency sound waves into the body and detects their echoes as they bounce off internal structures. The sound waves are then processed to form an image displayed on a computer monitor.

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In conventional 2D scanning the ultrasound image is made up of a series of thin slices and only one slice can be seen at any one time. With 3D ultrasound a volume of echoes is taken which can be stored digitally and shaded to produce life like pictures of the fetus. 4D just means that these life-like pictures can be seen to move in real time so the activity of the baby inside your womb can be studied.

Advantages of 3D and 4D ultrasound imaging

One of the advantages of 3D/4D imaging is that the examination time is shorter because the baby’s anatomy can be studied in any plane from the stored computer image.

Some parts of the baby’s anatomy can be seen much more clearly than with 2D ultrasound, especially the face, arms, legs, fingers and toes. Cleft palate has been shown to be more clearly seen with 3D ultrasound.

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In addition, activities of the baby inside the womb can be seen. With 4D scanning the fetus can now be seen to yawn, smile, swallow, blink and perform intricate finger movements. These activities can be seen in mid pregnancy although they become more common as pregnancy advances.

Bonding between parents and baby has been shown to be stronger because the picture of the baby is more realistic. Improved bonding has been shown to improve the mother’s care of herself and her baby.

Uses for antenatal ultrasound imaging

  • Diagnosing pregnancy
  • Determining fetal age
  • Diagnosing congenital abnormalities
  • Evaluating position of placenta
  • Determining multiple pregnancies

Obstetricians use ultrasound at a very low power level. When ultrasound is used by a qualified clinician to check for this kind of medical information, the medical benefit far outweighs any risk.

Is it safe?

Generally, ultrasonic fetal scanning is considered safe if properly used when information is needed about a pregnancy.

However, it is a form of energy. Even at low levels, laboratory studies have shown it can produce physical effects in tissue, such as jarring vibrations and a rise in temperature. Although there is no evidence that these physical effects can harm a fetus, the fact that these effects exist means that antenatal ultrasounds cannot be considered completely innocuous.

Animal studies have been performed during the last 30 years to investigate the effects of the procedure on a fetus, due to the increased use of obstetrical ultrasound. Most animal studies have not identified any fetal harm with low-dose ultrasound exposure.

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Human studies, however, are not feasible as it may be risky to subject unborn babies to any unknown effects. As technology advances, the potential for physical effects may be discovered in the future. A few studies suggest that exposure to diagnostic ultrasound during pregnancy may have an effect on human development, such as delayed speech in children.

The most consistent finding in the recent literature is a potential association between antenatal ultrasound exposure and subsequent left-handedness, especially among boys. At least three large follow-up studies involving thousands of school-age children in Sweden and Norway suggested such an association.

Modern ultrasound equipment is capable of producing approximately eight times higher intensities than equipment used a decade ago, it is important to continue studying the possible long-term effects of prenatal ultrasound in both animal and human.

With increasing mineralization of the fetal bone as the baby develops, the possibility of heating fetal bone increases. The procedure should be done prudently at the lowest possible energy output and for the least possible time especially on structures such as the fetal skull or spine.

Ultrasound images as souvenirs

As more advanced ultrasound technologies (usually using higher ultrasound intensities) become available, many expectant mothers are requesting fetal videos and portraits for souvenirs. The medical community is discouraging the use of ultrasound unless it is medically necessary.

Many world organizations of medical ultrasound advocate the responsible use of diagnostic ultrasound. They discourage the use of ultrasound for psychosocial purposes. The use of ultrasound to view the fetus, obtain a picture of the fetus or determine the fetal gender without a medical indication is not advisable.

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Although there are no confirmed biological effects on patients caused by exposures from present diagnostic ultrasound instruments, the possibility exists that such biological effects may be identified in the future. Thus ultrasound should be used in a prudent manner to provide medical benefit to the patient. In light of all that remains unknown, having an antenatal ultrasound for non-medical reasons is not a good idea.

For more information from Dr. Chew, visit aLife.org.sg, or ask him something on our Ask Our Experts page. Also, make sure you like us on Facebook and stay up-to-date on the latest from Pregnant.Sg!

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