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All about Ultrasound

By Dr Sarah Buckley

First Published in Australia’s Parents Pregnancy, Summer 1999

Ultrasound scanning was originally developed in World War II to detect enemy submarines. Its use in medicine was pioneered by Dr Ian Donald in Glasgow, who first used ultrasound to look at abdominal tumours, and later babies in utero in the mid 1950’s.(Oakley, 1986) Ultrasound in pregnancy spread quickly, and developments in this technology have lead to the use of "real-time" (i.e. moving) images, as well as doppler ultrasound, which is used in specialised scans, fetal monitors and hand-held fetal stethescopes ("sonicaids").

Ultrasound in pregnancy has become almost universal. In a 1994 Australia’s Parents survey, 99.5% of respondents reported having at least one ultrasound in their last pregnancy. The cost of such widespread use of obstetric ultrasound is enormous. In 1997-8, the government, via medicare, paid out $39 million for pregnancy ultrasound. The cost of all obstetric care for this year was $54 million.

Ultrasound may be offered to a pregnant woman in two situations- either to investigate a possible problem at any stage of pregnancy, or as a routine scan at around 18 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 or twins are suspected. In these cases, the information gained from ultrasound can be very useful in decision-making, and generally most professionals in the area would support the use of ultrasound in this context.

However the use of routine prenatal ultrasound (RPU) is more controversial, as this involves scanning all pregnant women in the hope of improving the outcome for some mothers and babies.

When RPU is used, there are four main areas of information that can be gained..

Firstly a due date may be estimated. Dating is most accurate at the early stages of pregnancy, when babies vary the least in size. At 18 to 20 weeks, expected date of delivery (EDD) is accurate to within a week either side. Some studies have suggested that an early examination, or a woman’s dates, can be as accurate as RPU. (Olsen and Clausen, 1997; Kieler et al, 1993)

Secondly, ultrasound is used to discover unsuspected physical abnormalities. While many women are reassured by a normal scan, in fact RPU detects only between 17% and 80%of the 1 in 50 babies that have major abnormalities at birth.(Ewigman 1993, Luck,1992) A recent Brisbane study showed that ultrasound at a major women’s hospital missed around 40% of abnormalities, with many of these being difficult or impossible to detect.(Chan et al, 1997) Major causes of intellectual disability such as cerebral palsy and Down’s syndrome are unlikely to be picked up on a routine scan, as are heart and kidney abnormalities.

When an abnormality is detected, there is a small chance that the finding is a "false positive" diagnoses, where the ultrasound is wrong, and the baby is, in fact normal. Even with the best equipment and operators, at least one in one hundred women who are told that their baby has major defects, will, in fact, have a normal baby.(Luck, 1992) In some instances, normal babies have been aborted because of false-positive diagnoses. (AIMS, 1993)

As well as false positives, there are also uncertain cases, where the ultrasound image cannot be easily interpreted, and the outcome for the baby is not known. In one study, almost 10% of scans were uncertain. (Sparling et al 1988) This can create immense anxiety for the woman and her family, and the worry may not be allayed by the birth of a normal baby. In the same study, mothers with "questionable" diagnoses still had this anxiety 3 months after the birth of their baby.

In some cases of uncertainty, the doubt can be resolved by further tests such as amniocentesis. In this situation, there may be up to two weeks wait for results, during which time a mother has to decide if she would terminate the pregnancy if an abnormality is found. Even mothers who receive reassuring news have felt that this process has interfered with their relationship with their baby. (see Brookes, 1995)

The third area in which ultrasound can give information is location of the placenta. A placenta which is very low-lying at birth (placenta praevia) puts mother and baby at risk of severe bleeding, and usually necessitates a caesarean section. However, 19 out of 20 women who have placenta praevia detected on RPU will be needlessly worried: the placenta will effectively move up, and not cause problems at the birth. (MIDIRS 1995) Furthermore detection of placenta praevia by RPU has not been found to be safer than detection in labour. (Saari-Kemppainen, 1990)

Lastly, ultrasound can detect the presence of more than one baby at an early stage of pregnancy. Again, there are no documented health advantages for mother or babies, and, without RPU, almost all multiple pregnancies are discovered before birth.(Informed choice for Professionals 1996)

Supporters of RPU argue that availability of this information should lead to better outcomes for mother and baby. While this would seem logical, researchers have not found evidence of significant benefit from RPU, and the issue of the safety of ultrasound has not yet been resolved (see below).

From a research perspective, the most significant benefit of RPU is a small reduction in perinatal mortality- the number of babies dying around the time of birth. However this is a statistical, rather than a genuine reduction. When a baby is found to have a fatal abnormality on RPU and the pregnancy is terminated, perinatal mortality is improved because deaths below 22 weeks are not counted in perinatal mortality statistics

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 from their "abnormal" baby. (Brookes, 1995).

Furthermore, there is no evidence that women who have chosen termination are, in the long term, psychologically better off than women whose affected baby has died at birth. In fact there are suggestions that the reverse may be true in some cases. (Watkins, 1989). In choosing a possible stillbirth over a termination, women at least get social acknowledgement and support, and are able to grieve openly. Where 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. (MIDIRS 1996)

When minor abnormalities are found, women can feel that some of the pleasure has been taken away from their pregnancy. Occasionally, minor abnormalities found on RPU have been seen to spontaneously resolve.

Another quoted benefit of RPU is a reduced risk of being induced for being "overdue", due to more certainty with RPU dating. Around one in 5 women have their dates changed by scan, and usually the date is put later.(MIDIRS, 1996) There is as yet no clear evidence that this leads to less women being induced, and the chance of induction is more determined by hospital or doctor policy than by availability of RPU. (MIDIRS 1996)

Many supporters of RPU claim that it is a pleasurable experience, and contributes to "bonding" between mother (and father if he is present) and baby. While it is true that it can be exciting to get a first glimpse of one’s baby in utero, there is no evidence that it helps attachment or encourages healthier behaviour towards the baby.(MIDIRS 1996)For many women the bonding comes naturally when they begin to feel movements at 16 to 20 weeks.

A number of studies have raised serious doubts about the safety of ultrasound for mother and baby, but studies are not yet definitive. The first study suggesting problems was a study on cells grown in the lab. Cell abnormalities caused by exposure to ultrasound were seen to persist for several generations.(Liebeskind 1979) Another study showed that, in newborn rats, ultrasound can damage the myelin that covers nerves,(Ellisman 1987) indicating that the nervous system may be particularly susceptible to damage from this technology. Studies on humans exposed to ultrasound have shown that possible adverse effects include premature ovulation (Testart 1982), preterm labour or miscarriage (Lorenz, 1990; Saari-Kemppainen,1990), low birth weight (Newnham, 1993), poorer condition at birth (Thacker 1985; Newnham, 1991), dyslexia (Stark et al 1984), delayed speech development (Campbell, 1993) and less right-handedness (Salvesen et al 1993: Kieler et al 1998). Non right-handedness is, in other circumstances, seen as a marker of damage to the developing brain. One Australian study showed that babies exposed to 5 or more ultrasounds were 30% more likely to develop intrauterine growth retardation (IUGR)- a condition that ultrasound is often used to detect. (Newnham, 1993)

Two long-term study comparing exposed and unexposed childrens’ development at 8 to 9 years old found no measurable effect from ultrasound. (Salvesen et al 1992, Kieler et al, 1998) However, as the authors note, intensities used today are many times higher than in 1979 to 1981. Further studies are obviously needed in this area, particularly in the area of Doppler ultrasound, where exposure levels are much higher.

A further problem with studying ultrasound’s effect is the huge range of output, or dose, possible from a single machine. Modern machines can give comparable ultrasound pictures using a lower, or a 5000 times higher dose (Meire, 1987), and there are no standards to ensure that the lowest dose is used. Because of the complexity of machines, it is difficult to even quantify the dose given in each examination.(Taylor, 1990) In Australia there is no requirement for training, and the skill and experience of operators varies widely.

In all the research done on ultrasound, there has been very little interest in women's opinions of RPU, and the consequences of universal scanning for a woman's experience of pregnancy. In 'The Tentative Pregnancy', Barbara Katz Rothman's thoughtful book on prenatal diagnosis, the author suggests that the large numbers of screening tests currently being offered to check for abnormalities makes every pregnancy 'tentative' until reassuring results come back.

Ultrasound is not compulsory, and I suggest that each woman consider the risks, benefits and implications of scanning for her own particular situation.

If you decide 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 and say that you want the shortest scan possible. If an abnormality is found, ask for counselling and a second opinion as soon as practical. And remember that it's your baby, and your choice.


AIMS UK. Ultrasound Unsound? AIMS Journal vol 5 no 1, spring 1993
Brookes, A. Women’s experience of routine prenatal ultrasound. Healthsharing Women: The newsletter of Healthsharing Women’s Health Resource Service. Vol 5, no’s 3 & 4. Dec 1994- March 1995.
Campbell JD et al Case-control study of prenatal ultrasonography in children with delayed speech. Can Med Ass J 1993 vol 149 no 10 pp1435-1440
Chan FY. Limitations of Ultrasound. Paper presented at Perinatal Society of Australia and New Zealand 1st Annual Congress, Freemantle 1997
Ellisman MH, Palmer DE, Andre MP. Diagnostic levels of ultrasound may disrupt myelination. Experimental Neurology 1987 vol 98 no 1 pp78-92
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Kieler H, Axelsson O, Nilsson S, Waldenstrom U. Comparison of ultrasonic measurement of biparietal diameter and last menstrual period as a predictor of day of delivery in women with regular 28 day cycles. Acta-Obstet-Gynecol-Scand, 1993 vol 75 no 5 pp 347-9
Kieler H, Ahlsten G, Haguland B et al. Routine ultrasound screening in pregnancy and the children’s subsequent neorological development. Obstet Gynecol 1998 vol 91 5 (pt 1) pp750-6
Kieler H, Axelsson O, Haguland B, et al. Routine ultrasound screening in pregnancy and the children’s subsequent handedness. Early Hum Dev 1998 , vol 50 no 2, pp233-245
Luck CA. Value of routine ultrasound scanning at 19 weeks: a four year study of 8849 deliveries. BMJ 1992, vol 34, no6840, pp1474-8
Liebeskind D, Bases R, Elequin F et al. Diagnostic ultrasound: effects on the DNA and growth patterns of animal cells. Radiology 1979 vol 131 no 1 pp 177-184
Lorenz RP, Comstock CH, Bottoms SF, Marx SR. Randomised prospective trial comparing ultrasonography and pelvic examination for preterm labor surveillance. Am J Obstet Gynecol 1990 vol 162 no 6 pp 1603-1610
Meire HB. The safety of diagnostic ultrasound.(commentary) Br J Obstet Gynaecol 1987 vol 94, pp1121-1122
MIDIRS. Informed Choice for professionals leaflet no 3. Ultrasound screening in the first half of pregnancy: is it useful for everyone? MIDIRS and the NHS centre for Reviews and Dissemination. 1996
Newnham J, Evans SF, Michael CA et al. Effects of frequent ultrasound during pregnancy: a randomised controlled trial. Lancet 1993, vol 342, no 8876, pp887-91
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Olsen O et al. Routine ultrasound dating has not been shown to be more accurate than the calendar method. Br J Obstet Gynaecol 1997, Vol 104 No 11 pp1221-2
Rothman, Barbara Katz. The Tentative Pregnancy: Amniocentesis and the Sexual Politics of Motherhod. (2nd ed) Pandora 1994
Saari-Kemppainen A, Karjalainen O, Ylostalo P et al. Ultrasound Screening and perinatal mortality: controlled trial of systematic one-stage screening in pregnancy. The Helsinki ultrasound trial. Lancet 1990 vol 336, no 8712. pp 387-391
Salvesen KA, Bakketeig LS, Eik-nes SH et al. Routine ultrasonography in utero and school performance at age 8-9 years. Lancet 1992, vol 339 no 8785 pp 85-89
Salvesen KA, Vatten LJ, Eik-nes SH et al. Routine ultrasonography in utero and subsequent handedness and neurological development. BMJ 1993: vol 307 no 6897 pp159-64
Sparling JW, Seeds JW, Farran DC. The relationship of obstetric ultrasound to parent and infant behavior. Obstet Gynecol 1988 vol 72 no 6. pp902-7
Stark CR, Orleans M, Havercamp AD et al.. Short and long term risks after exposure to diagnostic ultrasound in utero. Obstet Gynecol, 1984, vol 63 pp 194-200
Taylor KJW A prudent approach to ultrasound imaging of the fetus and newborn. Birth 1990. Vol 17 no 4, pp218-223
Testart J, Thebalt A, Souderis E, Frydman R. Premature ovulation after ovarian ultrasonography. Br J Obstet Gynaecol, 1982, vol 89, no 9, pp 694-700
Thacker SB. Quality of controlled clinical trials. The case of imaging ultrasound in obstetrics: a review. Br J Obstet Gynaecol, 1985 vol 92, no 5, pp 437-444
Watkins D. An alternative to termination of pregnancy. The Practitioner,1989, vol 233 no 1472,pp990, 992.

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