Every Tuesday, local experts field your questions about your health, your children's health and related issues. E-mail me if you have questions.

Today, Dr. Alice Chuang, an assistant professor of obstetrics and gynecology at UNC-Chapel Hill's School of Medicine and fellow of the American College of Obstetricians and Gynecologists, answers a question from a local mom who is expecting.

The question: Can you have too many ultrasounds during pregnancy? I received two gift certificates for 3D ultrasounds and I'm wondering if doing both is safe. I'm seven months pregnant.

The answer: In general, ultrasound is safe during pregnancy; even multiple ultrasounds are safe during pregnancy. I would refer you to the American Institute for Ultrasound in Medicine and their comments on this topic.

This is based on the data we currently have which predominantly looks at women who had medically indicated ultrasounds. We do not have research reflecting, for instance, daily ultrasound in pregnancy. (a la Tom Cruise purchasing an ultrasound and doing his own at home every day or more than every day.) AIUM states that we cannot consider ultrasound technology completely harmless, but when used to diagnose medical problems or to examine a fetus for medical reasons, the benefit outweighs the risk. Thus, ultrasounds in pregnancy are acceptable. Remember that ultrasound is a usually benign but potentially powerful technology. For example, currently very powerful ultrasounds are being used to destroy benign tumors called fibroids in the uterus. This is called magnetic resonance-guided focused ultrasound ablation (MRgFUS). (Duke offers this technology.) Granted, this type of ultrasonic technology is more powerful -- many, many times more powerful -- than that used to image fetuses, but it is used to destroy tissue. The point is that sound waves, when strong enough and focused enough, can destroy tissue. All medical technology should be used with respect and for appropriate purposes.

In terms of 3D ultrasound ... having a 3D ultrasound during pregnancy is usually a very special experience for the average mother and father. Having one is certainly not harmful, and for that matter, having two probably isn't either. I think it is important that one does not skip a medically indicated ultrasound (one ordered by a physician) in lieu of a 3D ultrasound. I have had patients who did not want to pay the copay for the ultrasound I ordered, but did go to a 3D ultrasound clinic to see their baby in 3D. This makes me uncomfortable because a 3D ultrasound does not examine the same things on a fetus. The goal of a 3D ultrasound is to provide the parents with nice 3D images of the fetus, particularly the face. A medically indicated ultrasound systematically examines the fetus's organs and measurements for anomalies, problems with growth and other things.

If you are going to have a 3D ultrasound, have it after 32 weeks or so when the fetus looks less like a fetus and more like an infant.

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