When I was pregnant with my first baby in 1990, I decided against having a scan. This was a rather unexpected decision, as my partner and I are both doctors and had even done pregnancy scans ourselves—rather ineptly, but sometimes usefully—while training in family physician (GP) obstetrics a few years earlier.
What influenced me the most was my feeling that I could lose something important as a mother if I allowed someone to test my baby. I knew that if a minor or uncertain problem showed up, which is not uncommon, I would be obliged to return again and again and that, after a while, I might feel as if my baby belonged to the system and not to me.
In the years since then I have had three more unscanned babies and have read many articles and research papers about ultrasound. Nothing I have read has made me reconsider my decision. Although ultrasound may sometimes be useful when specific problems are suspected, my conclusion is that it is at best ineffective, and at worse dangerous, when used as a screening tool for every pregnant woman and her baby.
The history of ultrasound
Ultrasound was developed during World War II to detect enemy submarines, and was later used in the steel industry. In July 1955, Glasgow surgeon Ian Donald borrowed an industrial machine and, using beef-steaks for comparison, began to experiment with the abdominal tumours that he had removed from his patients. He discovered that different tissues gave different patterns of sound wave ‘echo’, leading him to realise that ultrasound offered a revolutionary way to look into the mysterious world of the growing baby.
This new technology spread rapidly into clinical obstetrics. Commercial machines became available in 1963 and by the late 1970s ultrasound had become a routine part of obstetric care. Today, ultrasound is seen as safe and effective, and scanning has become a rite of passage for pregnant women in most developed countries. In Australia, it is estimated that 99 per cent of babies are scanned at least once in pregnancy, usually as a routine prenatal ultrasound (RPU) at four to five months. In the US, where this cost is borne by the insurer or privately, around 70 percent of pregnant women have a scan, and in European countries, it is estimated that 98 percent of pregnant women have an ultrasound, usually once in each trimester (third) of pregnancy.
However, there is growing concern as to its safety and usefulness. UK consumer activist Beverley Beech has called RPU ‘The biggest uncontrolled experiment in history’ and the
Cochrane Collaborative Database—the peak authority in evidence-based medicine—concludes:
‘…no clear benefit in terms of a substantive outcome measure like perinatal mortality [number of babies dying around the time of birth] can yet be discerned to result from the routine use of ultrasound… For those considering its introduction, the benefit of the demonstrated advantages would need to be considered against the theoretical possibility that the use of ultrasound during pregnancy could be hazardous, and the need for additional resources.’
The additional resources consumed by routine ultrasound are substantial. In 1997, for example, the Australian Federal Government paid out A$39 million to subsidise pregnancy scans; an enormous expense compared to the A$54 million paid for all other (Australian) Medicare obstetric costs, and this figure does not include the additional costs paid by the woman herself. In the US, an estimated US$1.2 billion would be spent yearly if every pregnant woman had a single routine scan.
In 1987, UK radiologist, HD Meire, who had been performing pregnancy scans for 20 years, commented:
The casual observer might be forgiven for wondering why the medical profession is now involved in the wholesale examination of pregnant patients with machines emanating vastly different powers of energy, which is not proven to be harmless, to obtain information which is not proven to be of any clinical value by operators who are not certified as competent to perform the operations.
The situation today is unchanged on every count.
What is ultrasound?
The term ‘ultrasound’ refers to the ultra-high frequency sound waves used for diagnostic scanning: these waves vibrate at 10 to 20 million cycles per second, compared to 10 to 20 thousand cycles per second for audible sound. Ultrasound waves are emitted by a transducer (the part of the machine that is put onto the body), and a picture of the underlying tissues is built up from the pattern of echo waves that return to the transducer. Hard surfaces such as bone will return a stronger echo than soft tissue or fluids, giving the bony skeleton a white appearance on the screen.
Ordinary scans use pulses of ultrasound that last only a fraction of a second, with the interval between pulses being used by the machine to interpret the echo that returns. In contrast, Doppler techniques, which are used in specialised scans, foetal monitors and hand-held foetal stethoscopes (Sonicaid) use continuous waves, giving much higher levels of exposure than pulsed ultrasound. Many women do not realise that the small machines used to monitor their baby’s heartbeat are actually using Doppler ultrasound, although with fairly low exposure levels.
More recently ultrasonographers have begun using vaginal ultrasound, where the transducer is placed high in the pregnant woman’s vagina, much closer to her developing baby. This is used mostly in early pregnancy, when abdominal scans can give poor pictures. However, with vaginal ultrasound there is little intervening tissue to shield the baby, who is at a vulnerable stage of development, and exposure levels are high. Having a vaginal ultrasound is not a pleasant procedure for the woman; the term ‘diagnostic rape’ was coined to describe how some women experience this procedure.
Another recent application for ultrasound is the nuchal (neck) translucency (NT) test, where the thickness of the skinfold at the back of the baby’s head is measured at around three months. A slight increase in the thickness of the nuchal fold makes a baby more likely, statistically, to have Down syndrome. When the baby’s risk is estimated to be over one in 250 to 300, a definitive test is recommended.
Around 19 out of 20 babies diagnosed as high risk by nuchal translucency will not turn out to be affected by Down syndrome, and their mothers will have experienced several weeks of unnecessary anxiety. A nuchal translucency scan does not detect all babies affected by Down syndrome.
Information gained from ultrasound
Ultrasound is mainly used for two purposes in pregnancy—either to investigate a possible problem at any stage of pregnancy, or as a routine scan at around 18 to 20 weeks.
If there is bleeding in early pregnancy, for example, ultrasound may predict whether miscarriage is inevitable. Later in pregnancy, ultrasound can be used when a baby is not growing, or when a breech baby or twins are suspected. In these cases the information gained from ultrasound can be very useful in decision-making for the woman and her carers. However, the use of routine prenatal ultrasound is more controversial, as this involves scanning all pregnant women in the hope of improving the outcome for some mothers and babies.
Routine prenatal ultrasound (RPU) also known as a morphology scan, is designed to check the size and integrity of the baby. The timing of routine scans (18 to 20 weeks) is chosen for practical reasons. It offers a reasonably accurate due date—although dating is most accurate at the early stages of pregnancy, when babies vary the least in size—and the baby is big enough to see most of the abnormalities that are detectable on ultrasound. However, at this stage, the expected date of delivery (EDD) is only accurate to a week on either side of the given date, and some studies have suggested that an early examination, or calculations based on a woman’s menstrual cycle, can be as accurate as RPU.
While many women are reassured by a normal scan, RPU actually detects only between 17 per cent and 85 per cent of the one in 50 babies that have major abnormalities at birth. A 1997 study from Brisbane, Australia, showed that ultrasound at a major women’s hospital missed around 40 per cent of abnormalities, with most of these being difficult or impossible to detect. Major causes of intellectual disability such as cerebral palsy and Down syndrome are unlikely to be picked up on a routine scan, as are heart and kidney abnormalities.
When an abnormality is reported, there is a small chance that the finding is a false positive, where the ultrasound diagnosis is wrong and the baby is, in fact, healthy. A UK survey showed that, for one in 200 babies aborted for major abnormalities, the diagnosis on post-mortem was less severe than predicted by ultrasound, and the termination was probably unjustified. In this survey, 2.4 per cent of the babies diagnosed with major malformations, but not aborted, had conditions that were significantly over or under-diagnosed.
There are also many cases of error with more minor abnormalities, which can cause anxiety and repeated scans, and there are some conditions which have been seen to spontaneously resolve.
As well as false positives, there are also uncertain cases, where the ultrasound findings cannot be easily interpreted, and the outcome for the baby is not known. In one study involving women at high risk, almost 10 per cent of scans were uncertain. This can create immense anxiety for the woman and her family, and this worry may not be allayed by the birth of a normal baby. In the same study, mothers with uncertain diagnoses were still anxious three months after the birth of their baby.
These uncertainties include the so-called ‘soft markers’; conditions that do not cause problems, but which are sometimes linked with more serious diagnoses such as Down syndrome. These include choroid plexus cysts in the brain, echogenic (a brighter ultrasound image than expected) bowel and heart areas, short femur, short humerus and pyelectasis of the kidney (enlargement of part of the kidney). Around one per cent of babies, for example, have a choroid plexus cyst but only one in 150 of these babies will have a chromosomal abnormality such as Down syndrome. Some experts have suggested that soft markers should only be disclosed to women at high risk of abnormality.
In some cases of uncertainty, the doubt can be resolved by further tests such as amniocentesis. In this situation, there may be up to a two-week wait for results, during which time a mother has to decide if she would terminate the pregnancy if an abnormality is found. Some mothers who ultimately receive reassuring news have felt that this process has interfered with their relationship with their baby.
As well as estimating the EDD and checking for major abnormalities, RPU can also identify a low-lying placenta (placenta praevia), and detect the presence of more than one baby at an early stage of pregnancy. However, 19 out of 20 women who have placenta praevia detected on an early scan will be needlessly worried; the placenta will effectively move up, and not cause problems at the birth. Furthermore, detection of placenta praevia by RPU has not been found to be safer than detection in labour. No improvement in outcome has been shown for multiple pregnancies either; the vast majority of these will be detected before labour, even without RPU.
The American College of Obstetricians and Gynecologists, in their guidelines on routine ultrasound in low-risk pregnancy, conclude:
‘In a population of women with low-risk pregnancies, neither a reduction in perinatal morbidity [harm to babies around the time of birth] and mortality nor a lower rate of unnecessary interventions can be expected from routine diagnostic ultrasound. Thus ultrasound should be performed for specific indications in low-risk pregnancy.’
Biological effects of ultrasound
Ultrasound waves are known to affect tissues in two main ways. Firstly, the sonic beam causes heating of the highlighted area by about one degree Celsius (1.8° F). This is presumed to be non-significant, based on whole-body heating in pregnancy, which seems to be safe up to 2.5º Celsius (4.5º F). Doppler scans, which use continuous waves, can cause more significant heating, especially in the baby’s developing brain.
The second recognised effect is cavitation, where the small pockets of gas that exist within mammalian tissue vibrate and then collapse. In this situation:
‘… temperatures of many thousands of degrees Celsius in the gas create a wide range of chemical products, some of which are potentially toxic. These violent processes may be produced by micro-second pulses of the kind which are used in medical diagnosis…’
The significance of cavitation effects in human tissue remains uncertain. However, a number of studies have suggested that these effects may be of real concern in living tissues. The first study suggesting problems was a study on cells grown in a lab. Cell abnormalities caused by exposure to ultrasound were seen to persist for several generations. A more recent study involving newborn rats, who are at a similar stage of brain development to humans at four to five months in utero, showed that ultrasound can damage the myelin that covers nerves, indicating that the nervous system may be particularly susceptible to damage from this technology.
Another animal study published in 2001 showed that exposing mice to dosages typical of obstetric ultrasound caused a 22 per cent reduction in the rate of cell division, and a doubling of the rate of apoptosis (programmed cell death) in the cells of the small intestine. Other researchers have found that a single ten-minute ultrasound exposure in pregnancy affects the locomotor and learning abilities of mice offspring in adulthood, with a greater effect from longer exposure time.
Experts in this area have expressed concern, especially in relation to exposure of the developing central nervous system, whose tissues are sensitive to damage by physical agents such as heat and ultrasound. Barnett notes that heating of the baby’s brain is more likely after the first trimester (three months), as the baby’s bone is more developed, and can reflect and concentrate the ultrasound waves. Barnett warns, ‘When modern sophisticated equipment is used at maximum operating settings for Doppler examinations, the acoustic outputs are sufficient to produce obvious biological effects.’
‘If exposure to ultrasound… does cause death of cells, then the practice of ultrasonic imaging at 16 to 18 weeks will cause loss of neurones [brain cells] with little prospect of replacement of lost cells… The vulnerability is not for malformation but for maldevelopment leading to mental impairment caused by overall reduction in the number of functioning neurones in the future cerebral hemispheres.’
Recent research has found that ultrasound also induces bleeding in the lung. The American Institute of Ultrasound in Medicine (AIUM) recently concluded:
‘There exists abundant peer-reviewed published scientific research that clearly and convincingly documents that ultrasound at commercial diagnostic levels can produce lung damage and focal haemorrhage [bleeding] in a variety of mammalian species… The degree to which this is a clinically significant problem in humans is not known.’
Studies on humans exposed to ultrasound have shown that possible adverse effects include premature ovulation, preterm labour or miscarriage, low birth weight, poorer condition at birth, perinatal death, dyslexia, delayed speech development, and less right-handedness. Non right-handedness (left-handedness and ambidexterity) is a consistent finding in many studies and is, in other circumstances, seen as a marker of damage to the developing brain. One Australian study showed that babies exposed to five or more Doppler ultrasounds were 30 per cent more likely to develop intrauterine growth retardation (IUGR)—a condition that ultrasound is often used to detect.
Two long-term randomised controlled trials in Sweden and Norway compared exposed and unexposed (or less exposed) children’s development at eight to nine years old, and found no measurable effect on growth, development and learning, However, as above, there was more non-right-handedness in the offspring. It is difficult to gain reassurance from these trials because, for example, in the Helsinki study, 77 percent of the supposedly unexposed group actually had a scan, and in the major branch of the Norwegian trial, scanning time was only three minutes. And, as the authors note, intensities used today are many times higher than in 1979–81.
A more recent randomised trial, comparing outcomes after single and multiple pregnancy (Doppler) scans, has produced some degree of reassurance, finding no differences in the learning and motor functions of offspring followed to eight years old. This study did not, however, include a group of unexposed children, so we do not know whether these children’s outcomes are actually normal. It is also noteworthy that almost 45 percent of the ‘single scan’ group received two or more scans. The researchers state, ‘…our results do not lessen our need to undertake further studies of potential bio-effects of prenatal ultrasound scans.’
A recent summary of the safety of ultrasound in human studies, published in May 2002, in the prestigious US journal, Epidemiology, suggested:
Continued research is needed to evaluate the potential adverse effects of ultrasound exposure during pregnancy. These studies should measure the acoustic output, exposure time, number of exposures per subject, and the timing during the pregnancy when exposure(s) occurred.
These authors concluded: ‘Until long-term effects can be evaluated across generations, caution should be exercised when using this modality during pregnancy.’
Ultrasound exposure and dose
As these authors imply, we need to know the exposure involved in all studies of ultrasound, but this is not easy to measure because there is a huge range of output, or dose, possible from a single machine. Ultrasound machines can give comparable pictures using a lower, or a 5,000 times higher, output and, because of the complexity of machines, it has been difficult to quantify the output for each examination.
Furthermore, the incredibly fine details that we are now seeing on scans come at the cost of substantial increases in output. Recent changes to US FDA regulations now allow operators to use ultrasound machines at very high outputs, exposing unborn babies to intensities up to eight times higher than previously allowed, provided the output is displayed on the machine.
This new regulation gives operators a worryingly high degree of self-regulation, and its success in protecting unborn babies from harm depends on an appreciation, by each operator, of complex biophysical interactions (which are not well understood) and of the risk-benefit involved in every examination. Such expectations may not be realistic; in Australia, the UK, US, and most other countries, ultrasonography training is voluntary, even for obstetricians, and the skill and experience of operators varies widely. It also seems that few operators are aware of research findings such as those mentioned above.
As the AIUM noted in 2000:
‘… the responsibility of an informed decision concerning possible adverse effects of ultrasound in comparison to desired information will probably become more important over the next few years.’
Women’s experiences of ultrasound
Women have not been consulted at any stage in the development of this technology, and their experiences and wishes are presumed to coincide with, or be less important than, the medical information that ultrasound provides. For example, supporters of RPU presume that early diagnosis and termination is beneficial to the affected woman and her family. However, the discovery of a major abnormality on RPU can lead to very difficult decision-making.
Some women who agree to have an ultrasound are unaware that they may get information about their baby that they do not want, as they would not contemplate a termination. Other women can feel pressured to have a termination, or at the least feel some emotional distancing, when their baby is diagnosed with a possible abnormality.
Furthermore, there is no evidence that women who have chosen termination for a baby with a lethal abnormality are, in the long term, psychologically better off than women whose babies have died at birth; in fact, there are suggestions that the opposite may be true in some cases. When termination has been chosen, women are unlikely to share their story with others and can experience considerable guilt and pain from the knowledge that they themselves chose the loss.
When a minor abnormality is found —which may or may not be present at birth, as discussed above—a woman can feel that some of the pleasure has been taken away from her pregnancy. And the process of prenatal diagnosis can cause harm to the baby if it generates a high degree of anxiety—and high levels of stress hormones—in the mother, especially in the first half of pregnancy.
Women’s experiences with ultrasound, and other tests used for prenatal diagnosis such as amniocentesis, are thoughtfully presented in the book The Tentative Pregnancy by Barbara Katz Rothman. The author documents the heartache that women can go through when a difficult diagnosis is made; for some women, this pain can take years to resolve (These issues are further explored in byronchild [now Kindred] Sept 04, number 11).
Ultrasound also represents yet another way in which the deep internal knowledge that a mother has of her body, and her baby, is made secondary to technological information that comes from an expert using a machine; thus the cult of the expert is imprinted from the earliest weeks of life.
Furthermore, by treating the baby as a separate being, ultrasound artificially splits mother from baby well before this separation is a physiological or psychic reality. This further emphasises our culture’s favouring of individualism over mutuality and sets the scene for possible—but to my mind artificial—conflicts of interest between mother and baby in pregnancy, birth and parenting.
Conclusions and recommendations
I urge all pregnant women to think deeply before they choose to have a routine ultrasound. It is not compulsory, despite what some may say, and the risks, benefits, and implications of scanning need to be considered by each mother for herself and her baby, according to their specific situation.
If you choose to have a scan, be clear about the information that you do and do not want to be told. Have your scan done by an operator with a high level of skill and experience (usually this means performing at least 750 scans per year), and say that you want the shortest scan possible. Ask them to fill out the form (or give you the information), and then sign it.
If an abnormality is found, ask for counselling and a second opinion as soon as practical. And remember that it’s your baby, your body and your choice.
First published in Nexus magazine, vol 9, no 6, October–November 2002. This version updated and published in Gentle Birth, Gentle Mothering: The wisdom and science of gentle choices in pregnancy, birth and parenting.
Published in Kindred, Issue 24, December 07
See also, Be Proactive with your Prenatal Care pubished as part of the same feature in Kindred.
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