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.
References:
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 Ewigman BG, Crane JP, Frigoletto FD et al. Effect of prenatal
ultrasound screening on perinatal outcome.RADIUS study group. N Engl J Med
. 1993 vol 329, no 12, pp821-7 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
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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,
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form analysis in high risk pregnancies: a randomised controlled trial. Br
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8-13 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
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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
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Eik-nes SH et al. Routine ultrasonography in utero and subsequent
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pp159-64 Sparling JW, Seeds JW, Farran DC. The relationship of
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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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