Obstetrical Sonography:
The Best Way to Terrify a Pregnant Woman

Roy A. Filly, M.D.

I have just reached the 30th anniversary of the first obstetrical sonogram I performed. Even having witnessed each of the technological advancements in sonography over those three decades, it is still difficult to comprehend the enormous improvements in image quality that have occurred. These improvements have brought sonography from a “promising” diagnostic tool to a mainstay of modern imaging. However, nowhere in medicine has this technique had a more profound impact than in the field of obstetrics. Thirty years ago there was essentially no such thing as obstetrical imaging and prenatal diagnosis was in its infancy.

During this time obstetrical sonography went from a medical oddity to a test of such great value that several European countries perform at least two obstetrical sonograms in every pregnant woman and 70% of modern American mothers have had a sonogram during their pregnancy (1,2). Obstetrical sonograms provide a wealth of useful information to the primary care giver. Some of these benefits are easily measured: accuracy of estimating menstrual age, accuracy of predicting twins, etc. Others are more difficult to measure but we all agree are nonetheless of great benefit. One of the most important of these is providing “reassurance” to the expectant mother. In our Obstetrical Department the phrase “for size and dates and general reassurance” seems to be pasted on nearly all sonogram request forms. Personally, the opportunity to say, “everything looks fine” to an expectant mother was one of the perks of my job. I can see the wave of relief wash across her face. It’s always a touching moment followed by “thank you, Doctor”.

Today, I no longer feel that way. There are a growing number of patients where I dread having to speak to her. I have reviewed the sonographer’s scans and they disclose a finding that will send the mother into a tailspin of confusion and worry. I’m not talking about holoprosencephaly or bilateral renal agenesis. I have a great deal of experience discussing such devastating diagnoses with pregnant women. And while the news is sad, I always feel that I am providing the family with a great service. Nothing can change the fact that her fetus has a mortal anomaly. There will necessarily be a grieving period and tears will undoubtedly flow, but beginning that grieving period at the earliest possible date in her pregnancy is “good medicine”. 

Tomorrow when I return to work the odds are I will have to speak to a mother-to-be about an “abnormality” that I see on her sonogram and I won’t know what to tell her. I am talking about “abnormal” findings on her sonogram which loosely fit under the general heading of “Down syndrome markers” (some are actually better as markers of other trisomy syndromes). I am not referring to atrio-ventricular canal or duodenal atresia. These are strong indicators that the Down syndrome may be present. But Down syndrome or not, the fetus still has a serious anomaly and the detection of that anomaly is a benefit. What I am afraid to encounter tomorrow is an “abnormality” which is not really abnormal: choroid plexus cysts (3-31), echogenic intracardiac foci (32-36), mild pyelectasis (37-41), and echogenic bowel (42-45) . If her fetus has one of these “abnormalities” but doesn’t have the Down syndrome, then her fetus is normal. Excuse me, I’m certain I will be criticized if I don’t tell the mother-to-be that in the absence of the Down syndrome and the presence of echogenic bowel she must worry about her fetus having cystic fibrosis, developing intrauterine growth restriction, having a premature birth, a fetus with a cytomegalovirus infection, or a fetus who may die in her womb (46-49). Alternatively, if her fetus has mild pyelectasis and a normal karyotype her newborn child is at risk for urinary tract problems, must take antibiotics after birth, get an extensive and uncomfortable work-up for vesico-ureteral reflux and must be followed-up for many months to ensure normalcy (50). 

The sheer numbers of papers written on the subject only add credibility to their importance (3-49). Certainly, some authors disagree as to the importance of one or the other of these findings (51,52). Unfortunately, the physician performing a routine sonogram and finding one of these “markers” is hard pressed to make a determination regarding which expert to believe. Inevitably they choose the “safest” path; at least, “safest” from a medico-legal perspective. The mother is simply going to have to deal with the possibility that her fetus may have the Down syndrome or worse.

These Down syndrome markers are common findings in normal fetuses, particularly the echogenic intracardiac focus (EIF). EIF occurs in approximately 5% (it is probably closer to 10%) of fetuses (53). The choroid plexus cyst occurs in 1-2% of fetuses (3), echogenic bowel occurs in approximately 1% of all second-trimester fetuses (44) (many more if high frequency transducers are employed) and mild pyelectasis in 3% of normal fetuses (54). If you have a busy sonographic practice seeing 10-20 pregnant woman daily, you will most likely see one or the other of these “abnormalities” every day.

The researchers that originally described these findings did so in women at high risk to have a fetus with the Down syndrome (55-65). These were pregnant women older than 35 years or who had a positive “triple marker” screening test for the Down syndrome. In this group of women the application of these findings increases the probability of finding Down syndrome fetuses and they perform admirably in this regard. However, these women have already been counseled that amniocentesis is appropriate in their case. They are having a sonogram in order to downgrade their risk to a level where they may appropriately forego amniocentesis (66-76). When examining a mother-to-be in this circumstance I fully recognize the value of identifying these “abnormalities” and can counsel these women appropriately that their already substantial risk is further increased if I find one or more of these features. More importantly to her, if no markers for the Down syndrome are found her level of risk may be significantly reduced (67, 72, 73).

But then investigators (with the best of intentions, I am certain) appear to have taken a misstep. These findings when seen in a woman with a low risk of having a Down syndrome fetus were used to upgrade her risk (40, 77). The consumers of this information, the physicians in the trenches, read these scientific papers and then identify these “abnormalities” during a routine sonogram. What are they to tell the patient? This woman hasn’t already been counseled. She is having a sonogram for “reassurance” (forget that now). Her husband, children and parents are with her. There is a party atmosphere. The videotape is rolling. Soon the giggling and finger pointing at the screen will cease. The questions will change abruptly from “is that the heartbeat?” or “is that the penis there?” to “are you saying that my child is going to be mentally retarded?”

Without doubt you have now added cost to the management of that pregnancy. The patient may choose to undergo amniocentesis. She may be referred to a prenatal diagnostic center for a detailed fetal sonogram and genetic counseling. The innumerable hours of counseling by primary care givers and general sonologists to explain the “meaning” of this finding are not counted in these additional costs (78). Nor are the heartaches of the parents-to-be counted in this cost analysis. If they forego the amniocentesis (clearly the correct choice, in my opinion) then they must live with residual doubt for the remainder of the pregnancy. Does my fetus have the Down syndrome? Maybe I should have had the amniocentesis. The enjoyment of the anticipation of the birth of their son or daughter is now replaced with anxiety.

Well you say, look at all the good these findings have accomplished. Some bad must go along with all that good. Possibly I am the exception (I doubt it), but I don’t see “all the good”. I am a simple-minded physician. I like it when a sonographic finding passes the “Thank God Test”. The Thank God Test is passed when I say to myself “thank God” for that finding. If I hadn’t seen it I would have completely missed this devastating abnormality. I have no instance in my recollection where one or the other of these abnormalities was the sole reason I was able to recognize a fetus with the Down syndrome in a low risk patient. (This presumes, of course, that a reasonably careful sonogram following the AIUM guidelines has been performed.) Obviously someone has had such an experience: just not me. From my vantage point the identification of these “abnormalities” in low risk women has crossed the line of “more harm than good”.

What are we trying to accomplish with the sonographic observation of “Down syndrome markers” in low risk women? Twenty percent of Down syndrome fetuses are born to mothers 35 years or older. We have known for many years that we must be suspicious in this group. Maternal serum screening programs for the so-called “triple markers” in women <35 years of age has become an effective screening test, with a sensitivity of 57% (79). Of the residual fetuses with the Down syndrome, sonographically apparent major anomalies are present in 25% - 33%. Further, of the residual fetuses with the Down syndrome a moderate number will simply die in utero. At birth, the incidence of trisomy 21 is 33% lower than it is at 15 - 20 weeks (80). Think about it! For the tiny residual number of Down syndrome fetuses that may potentially come to light by chasing down every last “marker” we intend to put at least 10% of all pregnant women with perfectly normal fetuses through a great deal of worry.

So then, what should I do tomorrow? Should I have the courage of my convictions and simply ignore these features? I wish I had that courage, but I don’t. Even with my considerable “clout” in the world of obstetrical sonography, I cannot unilaterally ignore the sonographic medical literature. That is not how American medicine works.

I am confident that I am not alone in my concerns regarding this issue. I further believe that the authors who did this excellent research in the “high risk” population are becoming aware that these features are not proving as beneficial in the “low risk” population as they had hoped. It is time for the American Institute of Ultrasound in Medicine or the American College of Obstetrics and Gynecology to convene a panel of experts to analyze the data on this issue and publish a position paper on the practicality of employing Down syndrome “markers” in low risk women at the soonest possible date. 

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