Safety and 3D Ultrasound.

Is 3D ultrasound safe?

I asked myself the very same questions when I was first considering starting this business. As a certified doula in my province, I am naturally sceptical of a lot of modern practices and technology, so I did a fair bit of research on the subject, trying to remain as unbiased as I could.

The main concerns historically with prenatal ultrasound have been with regards to two physiological effects that have been demonstrated from the procedure. One is from an increase in temperature in the tissues, and the other is from the physiological effects of the actual vibration on the tissues.

With regard to temperature increases, it had been proposed that increases in tissue temperatures from the ultrasound would cause developmental problems in the fetus. It has been observed and is widely acknowledged in the medical community, that increases in the neighbourhood of 4.5 to 5.7 degrees Celsius are dangerous, no matter what the cause, be it from environmental conditions leading to heat stroke or fever due to illness. There are primarily two types of ultrasound used clinically. One is Doppler ultrasound, which is used to measure the volume and movement of liquids such as fetal blood flow. The other is pulsed ultrasound, which is used to gather images. This is the type that we employ. Doppler ultrasound is the one to be most concerned with, as it sends a continuous signal which, if used completely inappropriately, can raise tissue temperatures around bone up to 5.7 degrees. This will happen if the probe is held in one position for an excessive amount of time, such as 5 to 10 minutes. Pulsed ultrasound is exactly what it sounds like. It sends pulses of ultrasound of very short duration which can raise the tissue temperature levels up to 1.2 degrees, well within the accepted margin of safety. The average person’s body temperature will raise more than that by having a hot bath.

Most studies on ultrasound effects were performed over twenty years ago, before the advent of modern computers. At that point in time, the intensity of the machine’s output was less than those designed today, raising concerns that modern machines might be more dangerous than the older models. However, in those days, the standard procedure was to turn on the probe and move it around until the technician saw a good picture, would hold the probe stationary while they took a still picture, move the probe to another spot, take another picture while holding the probe still, move on to another spot etc. So for 5 to 10 minutes, the machine was constantly on.

Modern ultrasound machines such as ours have built-in computers which monitor tissue temperature and will raise alarms if the temperature increases are approaching 1 degree so the technician can safely modify their technique. In addition, the way modern machines work is to have the probe on from 10 to 20 seconds while the computer records images every second or so. Then the probe is deactivated and the technician plays back the images looking for the good pictures. So in a thirty-minute session, the fetus may be exposed to only two to three minutes of actual ultrasound signals, thereby negating by a very large margin, the effects of a higher output. This makes the more modern machines, in my opinion, much better than the ones used in the studies.

The second physiological concern was the effect of the actual vibrations on the structure of the developing fetus. In the 80’s and 90’s several studies were done on pregnant mice to determine if there would be adverse effects on fetal development. The primary study quoted by people leery of the procedure was performed on mice and showed that there were variations in the migration patterns of embryonic cells in the nervous system for a period of time following the ultrasound procedure. Often times, in preliminary studies looking for adverse effects, the subject animals are exposed to extreme conditions in order to ascertain if there are correlations that need more rigorous study. The danger of these studies is when the lay reader then concludes that this extreme is the norm. An example would be if you made a person drink litres and litres of water in a short period of time. This would lead to a condition called hyponatremia, which is deadly. Therefore, you would conclude that drinking water is dangerous and would, therefore, stop the practice altogether. While this conclusion is obviously deeply flawed and the outcome quite obvious to most of us, it is much harder for the layperson to make these determinations with complicated studies.

So the problem with this one study so often quoted is that the mice were exposed to ridiculous amounts of ultrasound intensity for a ridiculously long period of time. Mice embryos are situated about 1/8 of an inch underneath the skin, as opposed to humans which are often 2 to 3 inches below the skin. A mouse itself is about three inches long. In this study, the mice were subjected to human-sized settings of the ultrasound machine, using a probe that was the size of the entire mouse, and the mice were exposed to for 5 minutes up to 7 hours. In human terms, to make this study comparable, the probe would have to be about 5 foot six inches long and set to penetrate to around 2 feet past the host’s body. Funnily enough, the mice exposed to the longest periods of super high-intensity ultrasound showed cellular migration abnormalities.

Other studies have shown similar flaws in their methodology. We know that high levels of stress can very negatively affect the health of a developing fetus. Many of these studies have the mice handled by humans, placed on their backs(their most vulnerable position), have their heads, feet and tail taped to the table, shaved, have ultrasound gel applied, and then left there unable to move for hours. Many of these studies don’t treat the control animals in the same way before making their comparisons.

So what about longitudinal studies? The problem with these type of studies is that they can only control for a few variables at a time. Some people have claimed that ultrasound might cause cognitive or behavioural problems in children, and try to support these claims with this type of study, IE. Children who have had ultrasounds in utero versus those that have not. The problem with these studies is that they did not look at co-factors. One very significant example of a co-factor not accounted for is found in the Clinical Journal of Psychiatry in 2016 which demonstrated that gestational exposure to acetaminophen (especially when the duration of exposure was 28 days or more) was associated with motor milestone delay, gross and fine motor impairments, communication impairment, impairments in internalizing and externalizing behaviours, and hyperactivity, all at age 3 years. A very recent large cohort study with a 12.7-year follow-up found that gestational exposure to acetaminophen was associated with an increased risk of autism spectrum disorder, but only when a hyper-kinetic disorder was also present 

So, if Tylenol for one, which is prescribed to most pregnant women as a safe painkiller can possibly cause autism and developmental problems, it needs to be eliminated as a co-factor in these studies. Do you think the maker of Tylenol is going to encourage follow up studies to that? So if the longitudinal studies into the effects of ultrasound did not take into account the results of the above two mentioned studies, and they did not, how can they possibly make an accurate causal determination?

The better studies I found almost all conclude that ultrasound if done properly, is exceeding safe.