Obstetrical Ultrasound - A Sinister Cause for Concern?
A few minutes later, our nurse came out of the room to tell me that the patient was VERY upset. Now, in our business, it is not at all unusual to discuss a pregnancy complication with a patient who maintains a stoic face throughout the discussion and then falls apart when left alone with the nurse, but I was a little surprised in this case because I thought the conversation had gone well, the condition was not serious, the baby was fine, and the patient herself had smiled and expressed gratitude for the clarity of the discussion. “It’s not what you think,” the nurse told me, “She wants to know why we didn’t do another ultrasound today because she always has one done at each of her OB visits in her doctor’s office...”
I had just reviewed her records, I knew she had had multiple ultrasounds performed in her provider's office, the most recent being just a few days before her visit with me, and according to her report and the office notes, “the baby was growing well and had no problems.” Now, you have to understand, as a specialist in Maternal-Fetal Medicine, much of my kids’ college educations are going to be funded by the many ultrasound-based procedures we perform on a daily basis. However, as part of my devotion to the admonition primum non nocere (above all, do no harm), I have always considered myself rather conservative in the number of ultrasound studies I perform and rarely will do one without some clinical indication. So, there was something that made me very uncomfortable about her request. And, to be honest with you, part of that discomfort was fueled by a recent query from one of our readers who asked me if it was true that ultrasound increased the risk that her baby would be lefthanded (we will return to that question in the next post).
Primum non nocere reminds us that we must consider the possible harm that any intervention might cause and that human acts with good intentions may have unwanted consequences. Although I do not have the statistics to back this up, I would wager that more than 80% of pregnant women in the U.S. today will have one or more ultrasounds done during their pregnancies. And this is not the first patient who has told me that an ultrasound was part of every prenatal visit. Ultrasound is so widely considered completely ‘safe’ that if you have enough money, like Tom Cruise, you can buy your own machine and use it every day; and “Fetal Foto” shops, employing 3-D and 4-D ultrasound imaging are springing up in strip malls all around the country for anyone who wants to pay cash to (possibly – no refund if they don’t get it) get a pretty picture of their baby before birth. But let me remind you that we also considered DES to be ‘safe’ and, indeed, many practitioners used it for years after it was recognized that it might not be.
In 2003 (Ultrasound Obstet Gynecol 2003;21:100), the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) reaffirmed an earlier “Safety Statement” in 2000 that “based on evidence currently available, routine clinical scanning of every woman during pregnancy using real-time B-mode imaging is not contraindicated.” This statement is predicated on the fact that ultrasound performed in the B-mode for routine 2-D, gray-scale imaging is conducted at very low levels of energy intensity and that in 40+ years of its use, no reproducible serious side-effects have ever been demonstrated.
However, ultrasound is ‘energy’ and its use is accompanied by the generation of heat (and other effects) and, indeed, it is widely used at higher intensities as a therapeutic modality in physical therapy (for which my left shoulder is very grateful, but my shoulder is not a baby). Furthermore, those of us who were trained during the era of ultrasound evolution tend to forget that not all ultrasound imaging for obstetrical purposes is created equal in terms of energy intensity. Our senses have been dulled by the mantra of ‘safety’ of B-mode scanning and have, without the data to back us up, extended the cavalier attitude to the routine and frequent use of both “spectral and color Doppler” for many diagnostic purposes in obstetrics that as the ISUOG statement reminds us “may produce high intensities…(and) because of high acoustic absorption by bone, the potential for heating adjacent tissues…”
It is true, we are given the admonition that “exposure time and acoustic output should be kept to the lowest levels consistent with obtaining diagnostic information and limited to medically indicated procedures, rather than for purely entertainment purposes.” But, by the same token, we have been given very little guidance over the years in terms of what that actually means. How many ultrasounds, how much exposure, how should exposure differ by gestational age? The human experiments have never been done, prospectively, and it is not realistic to think they will be at this point! But some observations related to ultrasound exposure fetal outcomes have been reported in obstetrical patients over the years and in our next post we will briefly discuss a few of those…