Are prenatal ultrasounds really safe and effective?

Prenatal imaging ultrasound.

Prenatal imaging ultrasound.

The Questionable Safety of Prenatal Ultrasound

Written by: Melissa Marks, LM, CPM

In the age of medical miracles and life-saving technology, the majority of women in industrialized countries would not even imagine going through their pregnancies without receiving at least one ultrasound scan.  Indeed, the first ultrasound is often seen as a sort of rite of passage into motherhood, with the photo printout of the baby in the womb serving as the trophy.  But what if pregnant women were warned of the potential dangers of ultrasound and doppler use?  What if their health care providers accurately explained both the risks and the benefits of prenatal ultrasound?  If all women were told all of the facts about the effects of ultrasound waves on the developing fetus, I believe many would choose to abstain from ultrasound exposure during pregnancy.  It is the responsibility and duty of maternity care providers to present this information to their clients.

What is ultrasound?

Ultrasound scanning uses ultra-high frequency sound waves traveling at 10 to 20 million cycles per second to create a picture from a pattern of echo waves.  The ultrasound waves are emitted by a transducer or ultrasound probe, which is the part of the ultrasound machine that is put directly onto the body.  Routine ultrasound scans use pulses of ultrasound waves that last a fraction of a second while doppler ultrasound, used to detect fetal heart tones (FHTs), use continuous ultrasound waves (Buckley 2005).

When and why is ultrasound used during pregnancy?

Pregnant women and their growing fetuses are generally exposed to ultrasound waves on approximately 12 or more different occasions through doppler use to detect FHTs at routine prenatal appointments, and at least once as part of a routine ultrasound scan at around 18 to 20 weeks to obtain an estimated due date, to detect possible genetic abnormalities, and to determine the position of the placenta.  A 3rd trimester ultrasound scan may be used to determine fetal position, to re-check placental placement, and/or to diagnose Intra-Uterine Growth Retardation (IUGR) through a series of 3rd trimester ultrasound scans (Buckley 2005).  Growing in popularity are so-called “ultrasound booths” which can be found in malls or at baby fairs and offer parents the opportunity to purchase keepsake ultrasound photos.  The staff that performs these non-medically-indicated keepsake ultrasound scans does not have to be medically trained in the usage of ultrasound equipment, and these ultrasound booths have already been banned in some states.

Has ultrasound been proven to be safe?

Because of widespread and physician-recommended use of prenatal ultrasound, it is generally assumed to be safe for both the pregnant mother and her unborn fetus.  However, two factors involved in the proposed safety of ultrasound include the dosage of ultrasound received by the fetus along with the skill of the operator.  Yet there are no national or international standards for the output characteristics of ultrasound equipment, and there is currently no mandatory training or certification for medical users of ultrasound apparatus (Wagner 1999).  What exactly does this mean?  UK radiologist H.D. Meire summed it up quite well in 1987 after having performed prenatal ultrasound scans for 20 years:

“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.” (Buckley 2005).

Simply put, ultrasound waves have never been proven to be safe for the developing fetus.  Furthermore, according to the World Health Organization, “[…] health technologies should be thoroughly evaluated prior to their widespread use.  Ultrasound screening during pregnancy is now in widespread use without sufficient evaluation.  Research has demonstrated its effectiveness for certain complications of pregnancy, but the published material does not justify the routine use of ultrasound in pregnant women.  There is also insufficient information with regard to the safety of ultrasound use during pregnancy.  There is as yet no comprehensive, multidisciplinary assessment of ultrasound use during pregnancy, including: clinical effectiveness, psychosocial effects, ethical considerations, legal implications, cost benefit, and safety.” (WHO 1984).

Doppler ultrasound uses continuous ultrasound waves to detect fetal heart tones.

Doppler ultrasound uses continuous ultrasound waves to detect fetal heart tones.

The Potential Dangers of Ultrasound

Miscarriage.  According to at least three separate studies, pregnant women who received two or more ultrasound scans during pregnancy had an increased risk of miscarriage (Beech 1999).  In one of these studies (a large randomized controlled trial from Helsinki) over 9,000 women were divided randomly into two groups: the members of the first group received an ultrasound scan between sixteen and twenty weeks.  The members of the second group received no scan.  The results of this study revealed that there were twenty miscarriages in the first group after the ultrasound scan, and no miscarriages in the second group (Saari-Kemppainen et al. 1990).  According to Beech, pregnant patients are not the only women at risk, however.  Physiotherapists who employ ultrasound therapy in their practice(s) are also at an increased risk of spontaneous abortion (Taskinen et al. 1990).

Intra-Uterine Growth Retardation.  In one large, randomized, controlled trial conducted in 1993, 1,415 pregnant women received an ultrasound scan at 18, 24, 28, 34, and 38 weeks gestation while the other half of the group, 1,419 pregnant women received only one ultrasound scan at 18 weeks gestation.  The alarming results revealed that the group that received multiple scans had a 30% increased risk of delivering an infant with intra-uterine growth retardation (Newnham, J. et al. 1993).

Indications of damage to the developing brain.  Studies have shown that prenatal ultrasound can lead to dyslexia, delayed speech development, and an increase in the incidence of left-handedness (Buckley 2005).  One specific study examining the effect of ultrasound exposure on pregnant mice found that “…exposure of the embryonic mouse to [ultrasound waves] can affect neuronal migration in the cerebral cortex and thereby prevent some neurons from attaining their final proper position.”  How is this study involving mice relevant to human fetuses?  The researchers state that “…the principal ultrasound beam characteristics (beam width, time-averaged intensity, and mechanical and thermal indices) used in this study were well within clinical norms for fetal exams.” (Ang, E.S., Jr., et al. 2006). 

Do the benefits of prenatal ultrasound outweigh the risks?

Diagnostic ultrasound has proven to be incredibly useful when used in investigating a suspected problem in pregnancy such as non-reassuring fetal heart tones or decreased fetal movement.  In regards to the routine use of ultrasound in pregnancy, however, the American Congress of Obstetricians and Gynecologists states, “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.” (Buckley 2005).  Furthermore, a randomized trial conducted by the RADIUS Study Group in 1993 concluded that routine screening ultrasound did not improve perinatal outcome as compared with selective use of ultrasound per clinician orders (Ewigman, B.G. et al. 1993). 

Are there alternatives to ultrasound and doppler use in maternity care?

Midwives and other maternity care providers can offer many alternative procedures to pregnant women wishing to forego ultrasound scanning and doppler use.

Fetal Heart Tone detection: Before handheld dopplers were affordable enough for every maternity care provider, the fetoscope was the tool of choice in detecting fetal heart tones (FHTs).  FHTs can be heard with the fetoscope at around 18 weeks gestation, compared to the doppler which can pick up FHTs as early as 12 weeks gestation.  However, the detection of FHTs via doppler ultrasound before 18 weeks gestation has never been proven to improve perinatal outcome and, as stated throughout this paper, may actually cause harm.  The fetoscope poses absolutely no threat to the developing fetus and as such, maternity care providers can listen to FHTs for the length of time needed to obtain an accurate FHT baseline without worrying about any potential dangers to the unborn child.

The fetoscope is a non-invasive auscultation tool and can be used to listen to fetal heart tones as early as 17-22 weeks of pregnancy.

The fetoscope is a non-invasive auscultation tool and can be used to listen to fetal heart tones as early as 17-22 weeks of pregnancy.

Accurate dating: When it comes to determining a woman’s estimated due date (EDD), midwives and other maternity care providers must learn to trust their pregnant clients as well as their own skills.  When women are sure of the date of their last menstrual period (LMP), it is important for their overall health, happiness, and emotional well-being to feel listened to and trusted by their maternity care provider.  If the pregnant woman knows an approximate time or a range of dates of her LMP, the midwife can compare that date range with other clinical findings, such as results of a bimanual examination and/or consecutive fundal height measurements, to pinpoint an estimated due date.  Maternity care providers must always keep in mind that regardless of how the estimated due date was established (whether by ultrasound, LMP, uterine size, or ovulation date), it is still just an estimate, and all fetuses develop at their own rate.

Placental placement: Routine ultrasound scans are often used to determine the placement of the placenta within the uterine cavity.  However, most routine scans are performed at around 18-20 weeks; this is a time in gestation where if placenta previa is diagnosed, 19 out of 20 cases will have resolved (the placentas move up with the growing uterus) by the end of term.  Furthermore, the detection of placenta previa prenatally has not been found to be safer than detection of placenta previa in labor (Buckley 2005).

Fetal positioning: Client education may prove to be the most useful tool the maternity care provider can use in determining fetal position.  Clients should be educated on the importance of optimal fetal positioning and how to prepare both the maternal and fetal body for labor and birth.  Clients can utilize posture and perform specific exercises to allow their unborn fetus the time necessary to adjust to being in the optimal occiput anterior position.  Midwives and other maternity care providers can become skilled at using their hands and the fetoscope to determine the position of the fetus.

The Right to Informed Consent

During the process of researching the topics presented in this paper, much conversation was brought up regarding a “woman’s choice”.  The current school of thought in modern midwifery and obstetrical care seems to assume that the use of obstetrical ultrasound and handheld dopplers will not decrease in number because pregnant women:  a) want reassurance that the baby is developing normally and b) to find out the gender of the baby.  It is so very important to understand, however, that these women often have absolutely no idea that there is some risk involved with ultrasound scans and doppler use.  Pregnant women often trust their maternity care providers with not only the lives of their unborn babies, but with their own lives, as well.  When this level of trust is involved in a healthcare setting, most women will not question the safety of any recommendation(s) the healthcare provider makes.

Midwives are often strong proponents of “informed consent”; that is, they believe that women have a right to know the risks and benefits of all tests and procedures before performing or referring for said test or procedure.  Without being aware of these risks and benefits, a woman cannot make a truly informed decision that is based on current research findings.  Midwives and other maternity care providers have a duty to their clients to keep up to date on the most current research and to present all findings to their clients.  Indeed, the World Health Organization “strongly endorses the principle of informed choice with regard to technology use.  The health-care providers have the moral responsibility: fully to inform the public about what is known and not known about ultrasound scanning during pregnancy; and fully to inform each woman prior to an ultrasound examination as to the clinical indication for ultrasound, its hoped-for benefit, its potential risk, and alternative available, if any.” (WHO 1984).

When a woman pregnant with a female baby is exposed to ultrasound waves, her baby daughter’s ovaries and eggs are also exposed.  This creates two subsequent generations of women exposed to ultrasound waves without their consent.  First, do no harm.     


Ang, E.S., Jr., et al. (2006). Prenatal exposure to ultrasound waves impacts neuronal migration in mice. PNAS, 103(34): 12903-10.

Beech, B. (1999). Ultrasound: Weighing the propaganda against the facts. Midwifery Today, 51.

Buckley, S. (2005). Ultrasound scans – cause for concern. Retrieved from

Ewigman, B.G. et al. and RADIUS study group. (1993). Effect of prenatal ultrasound screening on perinatal outcome. New England Journal of Medicine, 329, 12.

Newnham, J. et al. (1993). Effects of frequent ultrasound during pregnancy: A randomized controlled trial. The Lancet, 342, 887-90.

Rodgers, C. (2006). Questions about prenatal ultrasound and the alarming increase in autism. Midwifery Today, 80.

Saari-Kemppainen et al. (1990). Ultrasound screening and perinatal mortality: controlled trial of systematic one-stage screening in pregnancy.  The Lancet, 336, 387-91.

Taskinen, H. et al. (1990). Effects of ultrasound, shortwaves, and physical exertion on pregnancy outcome in physiotherapists. Journal of Epidemiology and Community Health, 44, 196-201.

Wagner, M. (1999). Ultrasound: More harm than good? Midwifery Today, 50.

World Health Organization. (1984). Diagnostic ultrasound in pregnancy: WHO view on routine screening. The Lancet, 2.