Prenatal Ultrasounds & Cavitation: Separating Facts From Fear

You might have seen the term “cavitation” while researching the safety of prenatal ultrasounds—and understandably, it may have raised concerns.

The idea of gas bubbles forming in your body sounds incredibly unsettling, especially during pregnancy. But what does cavitation actually mean in the context of prenatal ultrasound imaging? And is it something you should truly worry about?

Let’s take a closer look at what cavitation is, how it relates to prenatal ultrasounds, and what current research tells us about its safety.

What Is Cavitation in Ultrasounds?

Cavitation is a physical phenomenon that can occur when ultrasound waves move through liquid or soft tissue and create rapid pressure changes. These fluctuations can disturb the normal state of a fluid, potentially causing microscopic gas bubbles—if present—to form, grow, and, in some cases, collapse. Whether cavitation occurs and how it behaves depends on several factors, including the type of tissue, the presence of gas nuclei, the intensity of the ultrasound, and the frequency used.

There are two main types of cavitation:

Stable Cavitation: Bubbles gently oscillate (expand and contract) over multiple sound wave cycles without collapsing. This may occur in fluids without causing tissue damage.
Inertial (Transient) Cavitation: Bubbles expand rapidly and collapse with force. This type could generate intense local pressure and heat, which could theoretically harm nearby cells if it occurred in a living body.

While this might sound alarming, cavitation is not always a bad thing. In fact, there are several medical and cosmetic contexts where it’s a desired effect.

When Cavitation Is Intentionally Used

Cavitation, including inertial cavitation, is intentionally induced in certain treatments where its mechanical effects are beneficial. These procedures involve high-intensity ultrasound and are carefully controlled by trained professionals. Examples include:

Lithotripsy: This non-invasive treatment uses focused ultrasound or shockwaves to break up kidney stones. Cavitation helps fragment the stones without surgery.
High-Intensity Focused Ultrasound (HIFU): Used in oncology and aesthetic medicine, HIFU destroys targeted tissue (such as tumors or uterine fibroids) by creating localized heating and pressure, often with the help of cavitation.
Ultrasound Fat Reduction (Body Contouring): Sometimes marketed as “ultrasound cavitation,” this cosmetic treatment uses low-frequency ultrasound at high intensities to disrupt fat cell membranes, relying on cavitation in fat tissue to produce results.

In all of these cases, ultrasound is used at much higher energy levels than what’s typical of diagnostic imaging. These therapies are designed to change tissues in very specific ways and are performed under clinical protocols that account for (and even rely on) cavitation effects.

Cavitation and Prenatal Ultrasounds: What Research Shows

Cavitation can occur under certain conditions, but ongoing research has found that diagnostic ultrasounds, including those performed in pregnancy, do not create such conditions. Two primary reasons help explain this: the absence of cavitation nuclei and the low acoustic pressures used in prenatal ultrasound.

Prenatal ultrasound and the lack of cavitation nuclei

Cavitation, whether stable or inertial, requires the presence of gas-filled microbubbles or cavitation nuclei within the tissue or fluid being scanned. A 2023 study published in the National Library of Medicine titled “A Review on Biological Effects of Ultrasounds: Key Messages for Clinicians” found no evidence of such nuclei in vivo in gas-free tissues scanned during diagnostic ultrasounds. Internal factors like tissue viscosity and elasticity appear to further reduce the likelihood of cavitation occurring under diagnostic conditions.

These findings are also supported by additional research titled “Safety Assurance in Obstetrical Ultrasound,” which reports no evidence of inertial cavitation in the fetus during diagnostic ultrasound. The absence of cavitation nuclei in mammalian tissues is identified as the primary reason for this low risk.

While cavitation is a documented phenomenon in high-intensity procedures (such as lithotripsy, where bubble collapse is intentionally induced to fragment kidney stones), these acoustic conditions do not apply to routine prenatal imaging. Cavitation is also more likely in gas-containing tissues (like the lungs or intestines) or when contrast agents introduce gas microbubbles into the body, neither of which are present in prenatal scans.

Acoustic limits of prenatal ultrasound

"A Review on Biological Effects of Ultrasounds: Key Messages for Clinicians" also posits that cavitation (especially inertial cavitation, where bubbles rapidly collapse) requires a particular combination of bubble size, acoustic frequency, and pressure. At diagnostic ultrasound frequencies (typically 1–10 MHz), a gas bubble would need to be just a few microns in diameter to respond. However, the acoustic pressure needed to cause those bubbles to collapse far exceeds what diagnostic ultrasound delivers.

Modeling studies show that cavitation in soft tissue without gas nuclei would require pressures above 4 megapascals (MPa)—well beyond the output used in prenatal imaging. In other words, even if the right-sized bubbles were present, the energy from diagnostic ultrasound still wouldn’t be enough to cause collapse.

Continued research and clinical oversight

It’s important to note that ultrasound safety remains an active area of research. Scientists continue to evaluate the mechanical and thermal effects of ultrasound exposure to ensure that guidelines remain up to date. However, based on decades of laboratory and clinical data, the current scientific consensus is that routine prenatal ultrasound does not produce the conditions necessary for cavitation to occur.

Safety Measures in Prenatal Ultrasounds

Alongside the biological factors that limit cavitation risk, prenatal ultrasounds are performed under carefully regulated safety protocols. Diagnostic imaging systems are calibrated to use the lowest possible acoustic output while still producing medically useful images. This practice is guided by the ALARA principle—“As Low As Reasonably Achievable”—which minimizes unnecessary exposure while maintaining clinical effectiveness.

Two key indicators help monitor ultrasound safety in real time:

Mechanical Index (MI) estimates the likelihood of mechanical effects, including cavitation. It reflects the relationship between the peak ultrasound pressure and the frequency of the wave. A lower MI means a lower chance of mechanical effects.
Thermal Index (TI) estimates the potential for tissue heating during an ultrasound exam. It represents the ratio of the power used to the power required to raise tissue temperature by 1°C.

Both values are commonly displayed on the ultrasound screen and monitored by trained sonographers and physicians throughout the exam. These indices ensure that every scan remains within internationally recognized safety limits. In addition, professional organizations such as the American Institute of Ultrasound in Medicine (AIUM) and The American College of Obstetricians and Gynecologists (ACOG) regularly review and update guidelines to reflect the latest research.

Feel Confident in Your Prenatal Imaging

When you’re expecting, feeling confident in your care makes all the difference. Research continues to show that diagnostic ultrasound is a safe and trusted part of pregnancy monitoring, offering valuable insights without exposing you or your baby to unnecessary risks like cavitation.

At Nola Diagnostic Ultrasound, we’re here to provide clarity, reassurance, and expert imaging grounded in the latest safety standards. We proudly serve families throughout Greater New Orleans with care that’s both evidence-based and deeply supportive—because you deserve to feel at ease every step of the way.

To learn more about our approach to prenatal ultrasounds, feel free to get in touch with us today.