One of the most common questions I hear asked as an ultrasound technologist is, “Is ultrasound safe during pregnancy?” Expectant mothers and parents-to-be want to make sure they are not exposing their unborn baby to any potential harm. This is of course a very valid question – your protective parenting instincts are strong, and you have every right to be informed and educated so that you can ensure you are making the best decisions for you and your family. In this post, we will dive into the research surrounding its safety. But before we get into all that, let’s take a step back and briefly go over what ultrasound is and how it works.

How it Works

Ultrasound machines can generate an image of internal body structures by using high-frequency sound waves outside the range of human hearing. The ultrasound transducer, or probe (this is what the technologist uses to take pictures) contains small crystals made from a special material that exhibits specific “Piezoelectric” properties.

Back in the day, they used quartz, but now they are more commonly made of a ceramic called lead zirconate titanate. When the crystals come into contact with an electrical current, they change shape. This changing of shape causes them to vibrate and as a result, a sound wave is produced. This is called the “Piezoelectric Effect.” This sound wave, more commonly known as ultrasound, travels through tissue and back to the probe in the form of echoes. When the pressure from the sound wave hits the crystals, they generate an electrical charge (this is the “Reverse Piezoelectric Effect”) and the machine uses that electrical information to create an image.

3D ultrasound imaging works in much the same way as 2D in terms of the acoustic properties of the sound beam – it is not stronger or more powerful, the same parameters are being used. The only difference is the direction in which the beam is steered and how the machine interprets the incoming information.

Bioeffects: What are They?

When we talk about the safety of ultrasound, we are specifically referring to something called “bioeffects.” A bioeffect is a change observed in tissue in response to an outside force. Research done on the safety of ultrasound focuses on the two potential bioeffects. The first being “Thermal Bioeffects,” or any consequences observed from heating of the tissue and the second being “Non-Thermal Bioeffects” which would be related to a pressure change in tissue from the sound wave. If you’ve ever come across the term “cavitation,” that would fall under this category.

Cavitation

Cavitation is when gas bubbles are formed within a fluid due to the pressure changes from the sound wave. For this to occur, there needs to be an environment where air and fluid are in contact with one another. During pregnancy, your baby is living in a fluid-filled environment, receiving oxygenated blood through the umbilical cord. There is not yet exposure to air, thus eliminating any concerns of cavitation occurring during obstetrical ultrasounds.

Thermal Bioeffects

Thermal bioeffects, are, however, relevant in all types of ultrasound scans. Heating of tissue can occur through a process called “attenuation.” As the soundwave travels through the body, the intensity of it decreases due to multiple factors. These factors are collectively known as attenuation. They include anything that interferes with and weakens the sound beam, such as reflection and refraction. Absorption is another form of attenuation; this is the process in which the sound energy is converted to heat.

Safety Research

Many studies have been conducted over the years to determine if a rise in tissue temperature during obstetrical ultrasounds results in any type of adverse side effects for mother or baby. Researchers have evaluated potentially negative effects on a vast array of features, such as birth weight, auditory impairment, cognitive development, academic achievement, and mortality. Results from the properly controlled studies do not show any evidence of harm resulting from ultrasounds performed during pregnancy. The only reliable finding that has come out of decades of research is a tendency for left-handedness in males (1 in 20 were reported as displaying “non-righthandedness”), which is not inherently negative.

It is also important to realize that with many of these studies, the conditions are often not identical to what would take place in a real-world obstetrical scan. The exposure used during animal studies is often more intense for a longer duration of time, with a larger volume of tissue being affected. When an ultrasound is being performed, the transducer is constantly being moved around rather than sitting idle in one spot for an extended period. The tissue is not being subjected to a continuous stream of ultrasound; anytime the technologist freezes the image to evaluate it, change settings, take measurements, or adjust a 3D rendering, the use of ultrasound is paused, and the transducer remains inactive until the technologist again goes “live”.

In rat studies, the size of the ultrasound transducer is significant in relation to body size, whereas in a human mother, just a small percentage of overall body mass is being exposed. The baby is also surrounded by fluid and liquid has a very low absorption rate, meaning that it does not experience a significant increase in temperature from thermal bioeffects.

Scanning Precautions

Despite the lack of evidence for any negative effects resulting from ultrasound use during pregnancy, a properly trained technologist will still exercise an abundance of caution. The potential for an increase in tissue temperature can be monitored using a machine setting called, “Thermal Index”. The Thermal Index provides information about the maximum rise in tissue temperature that may be experienced if the scan were to continue for a period of time at the current settings; and even then, it doesn’t mean that a temperature raise of that degree will be seen, it is only stating the potential risk.

A diligent technologist will monitor this throughout the scan to ensure that it remains below a set threshold. They will also be especially prudent when it comes to using a setting called spectral Doppler – this is what is used to hear baby’s heart rate. It is a continuous wave of sound sent out at a higher level of power than what is used for 2D imaging. For those reasons, its use during the first trimester (when baby is more vulnerable) is usually limited, and it is only turned on for a specific diagnostic reason.

3D Ultrasounds

When it comes to ultrasounds performed at 3D imaging boutiques (non-diagnostic locations), the medical community hesitates to advocate for their safety due to indirect risks that may present themselves. If scans are performed by someone other than a properly trained technologist, the worry is that conservative scanning techniques will not be implemented, and machine settings will not be monitored.

There is also the possibility of normal anatomy being misinterpreted as abnormal, which could result in added unnecessary stress for parents, or alternatively, abnormal findings going unrecognized. (This risk is also present with diagnostic scans – misdiagnosis is arguably the most common cause of ultrasound-related safety concerns).

Some also express concerns that the mother may forego any recommended diagnostic scans because a “pretty,” normal appearing 3D image of baby’s face has given them the false sense of security that baby is, in fact healthy.

These situations can be avoided, however, and over the years, ultrasound has repeatedly proved itself as a safe and effective imaging tool. If having a 3D ultrasound during your pregnancy is something that interests you, I would highly recommend you seek out a location that employs registered technologists (ARDMS if you are in the United States and CRGS if you’re in Canada) who have experience in performing diagnostic obstetrical ultrasounds. This ensures that the person scanning you is both properly trained and has the necessary experience needed to recognize any potential abnormality that may be found.

I would also strongly advise against having additional, optional ultrasounds during the first trimester and suggest not booking in for your 3D scan until after you’ve had an ultrasound with your Doctor. This way, any concerns that may present themselves will have already been addressed and discussed with your Doctor in a proper medical setting. So, on the day of your 3D scan, you can fully relax and enjoy your ultrasound without worry now that the diagnostic portion is out of the way!

Pregnancy is an amazing adventure – it may also be the most significant event you will ever experience in your life! Receiving proper medical care throughout is extremely important (after performing high-risk obstetrical ultrasounds for the past 6 years, I know this all too well) but I think it is equally as important to remember that pregnancy is not an illness, and your entire experience should not be limited to a doctor’s office, a cold clinic, or a sterile hospital environment. There should also be moments set aside with the sole intent of just experiencing, bonding, and enjoying this special time!

Is Ultrasound Safe During Pregnancy?