Questions about Prenatal Ultrasound and the Alarming Increase in Autism
by Caroline Rodgers
© 2006 Midwifery Today, Inc. All rights reserved.
[Editor's note: This article first appeared in Midwifery Today Issue 80, Winter 2006.]
In May 2006, figures from the Centers for Disease Control (CDC) confirmed what too many parents and educators already knew: The incidence of autism is high, making it an "urgent public health issue," according to Dr. José Cordero, director of the CDC's National Center on Birth Defects and Developmental Disabilities. Only 12 years ago autism spectrum disorder (ASD) was so rare that it occurred in just one in 10,000 births.(1) Today ASD, which is characterized by a range of learning and social impairments, now occurs in one in 166 children (2)—with no sign of leveling off.
The steep increase in autism goes beyond the US: It is a global phenomenon, occurring in industrialized nations around the world. In the UK, teachers report one in 86 primary school children has special needs related to ASD.(3)
The cause of autism has been pinned on everything from "emotionally remote" mothers (since discredited) to vaccines, genetics, immunological disorders, environmental toxins and maternal infections. Today most researchers theorize that autism is caused by a complex interplay of genetics and environmental triggers. A far simpler possibility worthy of investigation is the pervasive use of prenatal ultrasound, which can cause potentially dangerous thermal effects.
Health practitioners involved in prenatal care have reason to be concerned about the use of ultrasound. Although proponents point out that ultrasound has been used in obstetrics for 50 years and early studies indicated it was safe for both mother and child, enough research has implicated it in neurodevelopmental disorders to warrant serious attention.
At a 1982 World Health Organization (WHO) meeting sponsored by the International Radiation Protection Association (IRPA) and other organizations, an international group of experts reported that "[t]here are several frequently quoted studies that claim to show that exposure to ultrasound in utero does not cause any significant abnormalities in the offspring. …However, these studies can be criticized on several grounds, including the lack of a control population and/or inadequate sample size, and exposure after the period of major organogenesis; this invalidates their conclusions…."(4)
Early studies showed that subtle effects of neurological damage linked to ultrasound were implicated by an increased incidence in left-handedness in boys (a marker for brain problems when not hereditary) and speech delays.(5) Then in August 2006, Pasko Rakic, chair of Yale School of Medicine's Department of Neurobiology, announced the results of a study in which pregnant mice underwent various durations of ultrasound.(6) The brains of the offspring showed damage consistent with that found in the brains of people with autism. The research, funded by the National Institute of Neurological Disorders and Stroke, also implicated ultrasound in neurodevelopmental problems in children, such as dyslexia, epilepsy, mental retardation and schizophrenia, and showed that damage to brain cells increased with longer exposures.(7)
Dr. Rakic's study, which expanded on prior research with similar results in 2004 (8), is just one of many animal experiments and human studies conducted over the years indicating that prenatal ultrasound can be harmful to babies. While some questions remain unanswered, based on available information, health practitioners must seriously consider the possible consequences of both routine and diagnostic use of ultrasound, as well as electronic fetal heart monitors, which may be neither non-invasive nor safe. If pregnant women knew all the facts, would they choose to expose their unborn children to a technology that—despite its increasingly entrenched position in modern obstetrics—has little or no proven benefit?
Problems with Sound and Heat
One challenge that ultrasound operators face is keeping the transducer positioned over the part of the fetus the operator is trying to visualize. When fetuses move away from the stream of high-frequency sound waves, they may be feeling vibrations, heat or both. As the FDA warned in 2004, "ultrasound is a form of energy, and even at low levels, laboratory studies have shown it can produce physical effect in tissue, such as jarring vibrations and a rise in temperature."(9) This is consistent with research conducted in 2001 in which an ultrasound transducer aimed directly at a miniature hydrophone placed in a woman's uterus recorded sound "as loud as a subway train coming into the station."(10)
A rise in temperature of fetal tissue—especially since the expectant mother cannot even feel it—might not seem alarming, but temperature increases can cause significant damage to a developing fetus's central nervous system, according to research.(11) Across mammalian species, elevated maternal or fetal body temperatures have been shown to result in birth defects in offspring.(12) An extensive review of literature on maternal hyperthermia in a range of mammals found that "central nervous system (CNS) defects appear to be the most common consequence of hyperthermia in all species, and cell death or delay in proliferation of neuroblasts [embryonic cells that develop into nerve cells] is believed to be one major explanation for these effects."(13)
Why should neurodevelopmental defects in rats or other mammals be of concern to expecting women?Because, as Cornell University researchers proved in 2001, brain development proceeds in the same manner "across many mammalian species, including human infants."(14) The team found "95 neural developmental milestones" that helped them pinpoint the sequence of brain growth events in different species.(15) Therefore, if repeated experiments show that elevated heat caused by ultrasound damages fetal brains in rats and other mammals, one can logically assume that it can harm human brains, too.
In fact, the FDA and professional medical associations know that prenatal ultrasound can be dangerous to humans, which is why they have consistently warned against the non-medical or "keepsake" ultrasound portrait studios that have cropped up in malls throughout the country.(16)
The risks to the baby are potentially higher in commercial enterprises due to the higher acoustic output required for high-definition images, a potentially long session—as technicians hunt for suitable images—and the employment of ultrasound operators who may have no medical background or appropriate training. These variables, along with factors such as cavitation (a bubbling effect caused by ultrasound that can damage cells) and on-screen safety indicators that may be inaccurate by a factor ranging from 2–6 (17), make the impact of ultrasound uncertain even in expert hands. Quite simply, if ultrasound can injure babies, it can cause the same damage whether done for routine, diagnostic or "entertainment" purposes.
Elevated Maternal Temperatures Cause Birth Defects
Understanding what happens when the fetus's temperature increases, whether caused by an elevation in maternal core temperature or by the more local effect of ultrasound, is the key to appreciating prenatal ultrasound risks. An individual's body temperature varies throughout the day due to various factors such as circadian rhythms, hormone fluctuations and physical exertion. While people may have up to 1.5° F in each direction of what is considered a "normal" core temperature, the overall average among people is 98.6° F. An increase of only 1.4° F to 100° F can cause headaches, body aches and fatigue, enough to get the individual excused from work. A temperature of 107° F can cause brain damage or death.
A core temperature of about 98.6° F is important because that is the point at which many important enzyme reactions occur. Temperature affects the actual shape of the proteins that create enzymes, and improperly shaped proteins are unable to do their jobs correctly. As factors such as the amount of heat or duration of exposure increase, enzyme reactions become less efficient until they are permanently inactivated, unable to function correctly even if the temperature returns to normal.(18)
Because temperature is critical to proper enzyme reactions, the body has built-in methods to regulate its core temperature. For instance, when it is too low, shivering warms it up; when it is too high, sweating wicks off the heat. For obvious reasons, fetuses cannot cool off by sweating. However, they have another defense against temperature increases: Each cell contains something called heat shock (HS) proteins that temporarily stop the formation of enzymes when temperatures reach dangerously high levels.(19)
Complicating the issue is the fact that ultrasound heats bone at a different rate than muscle, soft tissue or amniotic fluid.(20) Further, as bones calcify, they absorb and retain more heat. During the third trimester, the baby's skull can heat up 50 times faster than its surrounding tissue (21), subjecting parts of the brain that are close to the skull to secondary heat that can continue after the ultrasound exam has concluded.
Elevated temperatures that might only temporarily affect the mother can have devastating effects on a developing embryo. A 1998 article in the medical journal Cell Stress & Chaperones reported that "the HS response is inducible in early embryonic life but it fails to protect embryos against damage at certain stages of development." The authors noted, "With activation of the HS response, normal protein synthesis is suspended…but survival is achieved at the expense of normal development."(22)
Autism, Genetics and Twin Studies
What does elevated body temperature have to do with autism? Geneticists are trying to crack the DNA mysteries behind ASD. Recently researchers linked two mutations of the same X chromosome gene to autism in two unrelated families, although they do not yet understand at what stage these genes were damaged.(23) Because sibling and twin studies show a higher prevalence of autism among children in families with one autistic child, geneticists expected to find inherited factors, but despite millions of dollars invested in the search, no clear explanation indicates that ASD is inherited. Perhaps scientists need look no further than at the thermal effects of ultrasound for many answers.
If prenatal ultrasound is responsible for some cases of autism, it stands to reason that if one twin were autistic, the other would have a high probability of being affected, since both would have been exposed to ultrasound at the same time. In both identical and fraternal twins, one twin could be more severely affected than the other if he or she happened to take the brunt of the heat or sound waves. In the case of fraternal twins, since autism strikes males between three to five times more often than females, the sex of the twins also could make a difference in outcome.
A 2002 study showed that simply being a twin substantially increased the likelihood of autism, making twinning a risk factor.(24) Could this increased twin risk factor have to do with the practice of giving mothers with multiple gestations more ultrasounds than those expecting single births? While not discounting the role genetics may play in autism, the possible impact of prenatal ultrasound deserves serious consideration.
Ultrasound Warnings Unheeded
The idea that a prenatal ultrasound can be hazardous is not new. The previously mentioned 1982 WHO report, in its summary "Effects of Ultrasound on Biological Systems," stated that "…animal studies suggest that neurological, behavioral, developmental, immunological, haematological changes and reduced fetal weight can result from exposure to ultrasound."(25)
Two years later, when the National Institutes of Health (NIH) held a conference assessing ultrasound risks, it reported that when birth defects occurred, the acoustic output was usually high enough to cause considerable heat.(26). Although the NIH has since stated that the report "is no longer viewed…as guidance for current medical practice," the facts remain unchanged.
Despite the findings of these two major scientific gatherings, in 1993 the FDA approved an eight-fold increase in the potential acoustical output of ultrasound equipment (27), greatly increasing the possibility of disastrous pregnancy outcomes caused by overheating. Can the fact that this increase in potential thermal effects happened during the same period of time the incidence of autism increased nearly 60-fold be merely coincidental?
And here is a great blog with some wonderful insight into this subject:
http://jerobison.blogspot.ca/2012/05/more-thoughts-on-ultrasound-questions.html
And a snippet from the article which the Calgary Herald ran, for your viewing pleasure:
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