Dr. Greene's Answer
Prenatal ultrasounds are widely touted as a completely safe way to see the baby before birth. Before I tell you the latest information on ultrasounds in the medical literature, I’d like to tell you a little story:
In 1895, a German scientist named Wilhelm Conrand Roentgen was experimenting with cathode ray tubes and noticed something that other scientists had missed — a coated surface outside the tube would fluoresce even if shielded from visible or ultraviolet light from the tube. Roentgen concluded that he had stumbled onto some kind of invisible radiation. He named these mysterious new rays X rays.
It wasn’t long before X rays began to be used in medicine. One of the most famous pioneers of X radiography (taking pictures with X rays) was Marie Curie — a brilliant woman who won two Nobel Prizes. X rays were heralded as an entirely safe, painless, non-invasive way to view the inside of the human body. They were considered so safe that they were even used in shoe stores! People would try on a pair of shoes, have their feet X rayed inside the shoes to test the fit, and then try on another…
But Marie Curie died from X-ray-induced leukemia. In fact, many of the early pioneers of X ray research began developing cancer at a surprising rate, and X rays were found to be the cause. Now we know that X rays can be very beneficial, but that they are not without cost to our health. Prenatal X rays are associated with an 80% increase in the risk of childhood cancer (this effect diminishes drastically if the X ray is after birth).
Ultrasonography is still a very young science. The current Encyclopedia Britannica says, “Part of ultrasound’s usefulness is due to the fact that sound waves cause no damage to human tissues, unlike X rays. Because of its safety, ultrasound is most commonly used to examine fetuses in utero.”
Data is beginning to trickle in that this may not be entirely true.
Most of the studies looking at the effects of ultrasound on living tissue have shown no effect at all. But in Teratology (a journal looking at adverse effects of prenatal events) February 1993, a study of prenatal ultrasounds in macaque monkeys found a decreased birth weight, a decreased white blood count, and possibly a decrease in muscle tone in monkey babies whose mothers had received 10 minute ultrasounds five times a week during pregnancy weeks 4-6, then 3 times weekly during weeks 7-8, and weekly 20 minute ultrasounds thereafter. Similar, but more detailed, results were obtained in 1995.
In 1993, pregnant Swiss mice received diagnostic ultrasounds. Their offspring were slower learners at 3 months of age (Neurotoxicology and Teratology, Nov-Dec 1993). In 1994, pregnant rats in Cincinnati received daily 10 minute ultrasounds of varying intensity. Only those rats who received the highest intensity sound waves showed any effect — again slowed learning (Teratology, September 1994). In 1995, pregnant Swiss albino mice living in India received ultrasounds, of 10, 20, or 30 minute duration. Their offspring, as adults, showed less exploratory behavior and slower learning the longer their ultrasound exposure (Radiation Research, March 1995).
Studies in humans have never shown any behavioral changes. One randomized study of almost 3,000 Australian women who received normal ultrasounds at 18, 24, 28, 34, and 38 weeks gestation did demonstrate a lower birth weight of their children than the controls (Lancet, October 1993). An American study reviewed previous birth records of 13,000 pregnancies. This study looked specifically at the association of ultrasound exposure during pregnancy and the risk of low birthweight in the offspring. There was no indication of any adverse effect of prenatal ultrasound (American Journal of Perinatology, July 1994).
Another large study reviewed medical records and looked at rates of childhood cancer, neurologic problems, dyslexia, speech delay, left-handedness, and low birth weight in recipients of prenatal ultrasound. No associations were proven between ultrasound and any of these conditions, but there was insufficient data to reach a conclusion about left-handedness and low birth weight (Ultrasound in Obstetrics and Gynecology, October 1995).
In 1996 we received the first report of actual tissue damage in human fetuses after a one hour ultrasound. A repeat ultrasound 24 hours later revealed changes in the cell membranes and in the intracellular structures of the early fetuses. These changes disappeared within 3 days (Chung Hua Fu Chan Ko Tsa Chih, March 1996).
In answer to your specific question, Jane, I have never seen in the medical literature any report of a connection between ultrasounds and ear infections (if you hear any more, please let me know!). We do know that ultrasounds are very safe (far safer than X rays). We also know that sound wave energy does affect living tissue, but the full implications of this remain to be discovered. The ultrasound machines in common use keep changing (more quickly than the studies of long-term effects can possibly keep up with), as new technology allows clearer and clearer ultrasound pictures. We must respect what we do not yet know. Still, used judiciously, prenatal ultrasound is a truly wonderful tool.