4D ultrasound side effects: what is and isn’t known

What the FDA, ACOG, AIUM and ISUOG say

The FDA says ultrasound imaging “has an excellent safety record” and is “generally considered safe when used prudently by appropriately trained health care providers.” But “ultrasound energy has the potential to produce biological effects on the body” (FDA):

Ultrasound waves can heat the tissues slightly. In some cases, it can also produce small pockets of gas in body fluids or tissues (cavitation). The long-term consequences of these effects are still unknown.

U.S. Food and Drug Administration, 2024

The risks “may increase with unnecessary prolonged exposure to ultrasound energy, or when untrained users operate the device,” the FDA says. Using ultrasound “solely for non-medical purposes such as obtaining fetal ‘keepsake’ videos has been discouraged.”

• ACOG says ultrasound and MRI “are not associated with risk and are the imaging techniques of choice for the pregnant patient.” But they “should be used prudently and only when use is expected to answer a relevant clinical question or otherwise provide medical benefit to the patient” (ACOG Committee Opinion 723).
• The AIUM, the American Institute of Ultrasound in Medicine, finds “insufficient justification to warrant conclusion of a causal relationship between diagnostic ultrasound and recognized adverse effects in humans.” But the lack of conclusive studies “does not constitute proof that adverse effects are impossible.” It “strongly discourages the nonmedical use of ultrasound,” and counts only medical exams and teaching programs as ethical sources of keepsake images, not “freestanding commercial fetal imaging sites” like ours (AIUM).
• ISUOG and WFUMB, international ultrasound bodies, say there have been “no reported incidents of human fetal harm in over 40 years” of medically indicated, supervised use. But some biological effects “might, under certain circumstances, be detrimental” to a developing baby, so “the uncontrolled use of ultrasound without medical benefit should be avoided.” Both “disapprove of the use of ultrasound for the sole purpose of providing souvenir images” (ISUOG and WFUMB, 2011).

Why a medical scan is weighed differently

Each statement weighs ultrasound against a reason, and a medical scan has one. In the U.S., a medical scan after the first trimester checks the baby’s heart activity, fluid, placenta, anatomy and growth (ACR–ACOG–AIUM–SMFM–SRU). England’s 20-week scan looks “for 11 different conditions in your baby” (NHS).

A keepsake scan’s benefit is seeing your baby with your people (is it worth it?). The AIUM finds “only some scientific evidence that 3D sonography has a positive impact on parental-fetal bonding” (the bonding research). A keepsake 3D or 4D scan doesn’t check your baby’s anatomy, growth or health, or replace the anatomy scan. ISUOG has warned that souvenir-scan customers “often assume they have undergone a medical scan and may therefore forfeit a regular, scheduled medical scan” (ISUOG, 2009). What is an elective ultrasound? explains the difference.

How ultrasound affects the body: heat, gas pockets and two numbers

Sound, not X-rays

“Ultrasound exams do not use radiation (x-rays),” says RadiologyInfo.org. The FDA says ultrasound “is based on non-ionizing radiation, so it does not have the same risks as X-rays,” and calls 4D “3D ultrasound in motion.” Sound still carries energy, which in laboratory studies can cause “pressure oscillations” and a “rise in temperature” in tissue, the FDA says.

Heat and the thermal index (TI)

The TI estimates possible heating under model conditions (Health Canada). From 10 weeks, the U.S. practice guideline calls for the bone index (TIB), “when bone ossification is evident,” and says “A TI ratio of 0.7 or less should be used for obstetrical scanning” (ACR–ACOG–AIUM–SMFM–SRU).

Time counts too. Health Canada’s 2001 guidelines called the heating risk from ordinary B-mode imaging “negligible” on the evidence then. In Doppler and other modes, risk “depends on the temperature elevation and the dwell time,” how long one spot stays in the beam.

Gas pockets and the mechanical index (MI)

The MI shows “the relative potential for ultrasound to induce an adverse bio effect by a non thermal mechanism such as cavitation” (BMUS). Within recommended limits, Health Canada says, “mechanical effects are far less likely to be important in obstetrical ultrasound because of the absence of gas bodies.”

In its Doppler guideline, ISUOG says both numbers “should be displayed on the ultrasound screen” and the ALARA principle, “as low as reasonably achievable,” applied (ISUOG, 2021). BMUS defines that as “the lowest output power and the shortest scan time consistent with acquiring the required diagnostic information.” Is an early ultrasound safe for the baby? covers the first trimester.

Does a 4D scan mean more exposure than a 2D scan?

A 3D or 4D picture is built from ordinary 2D (B-mode) images (how each is made). A 2016 review in the Journal of Perinatal Medicine says 3D uses “repeated scans of multiple planes within a few seconds,” and 4D repeats those 3D images “in short intervals” (Pooh and colleagues).

A team led from Rush University Medical Center in Chicago measured the difference in 40 scans of patients booked for anatomy or follow-up exams, at a mean of 31 weeks. The TI averaged 0.27 in 3D, 0.24 in 4D and 0.28 in 2D, which the authors called “comparable,” and the MI was lower during 3D captures. Adding 3D took about 2 minutes of scanning, and 4D about 2.2 (Sheiner and colleagues, 2007).

The sources point to three things that change exposure:

• Time. The FDA says risks “may increase with unnecessary prolonged exposure.” The 2016 review says 4D exposure “should be shorter than 30 min.”
• Settings. The review wants both indices “lower than 1.0,” and the U.S. guideline 0.7 or less for the TI.
• Doppler. Pulsed and color Doppler add output, and when Doppler is combined with 3D or 4D, the review says, Doppler’s limits apply.

The Rush team noted in 2007 that “there are no studies regarding the safety of 3D ultrasound.” We found no later study of children after keepsake 3D or 4D sessions.

What studies of children have found

The trials below compared more scans with fewer, and their abstracts don’t mention 3D or 4D. The one study that isn’t a trial, a Boston case-control study, timed 3D and 4D imaging, but its abstract reports no result for it.

• Birth weight. In Perth, Australia, 2,834 women pregnant with one baby were randomized at 16 to 20 weeks to five scans with Doppler, from 18 to 38 weeks, or one scan at 18 weeks, with outcomes for 99%. The five-scan group had more growth-restricted babies (relative risk 1.35 for birth weight below the 10th percentile). The authors said it might be chance, or frequent exposure “may have influenced fetal growth.” They advised restricting repeated scans and Doppler studies to women for whom the information “is likely to be of clinical benefit” (Newnham and colleagues, 1993). At follow-up to age 8 (75% of 2,714 children), the groups were similar in size from age 1. At no age did standard tests of speech, language, behavior or neurological development show significant differences pointing to harm (Newnham and colleagues, 2004).
• Handedness. After two Norwegian trials of routine scanning in 1979–81, 2,161 of 2,428 eligible children (89%) were followed at 8 to 9. Left- or mixed-handedness was more common in the scanned group (odds ratio 1.32), with no link to impaired neurological development in the first year of life. The authors said the result “may be due to chance,” but that the hypothesis “may have some merit and should be tested in future studies” (Salvesen and colleagues, 1993). Across the trials in a WHO review, there was “a weak association” in boys (odds ratio 1.26) (Torloni and colleagues).
• Hearing and vision. Hearing (pure-tone audiometry) and eyesight tests at 7, and parents’ reports, showed no significant differences in the Norwegian children (Salvesen and colleagues, 1992).
• Reading and school. In Norway, 603 children took dyslexia tests: 7% of the scanned group and 9% of controls tested as dyslexic, and their scores didn’t differ (Salvesen and colleagues, 1992). In Sweden, grades at 15 to 16 for 4,458 teenagers (94%) from a 1985–87 trial showed “in general” that second-trimester scans had “no effect on overall school performance.” Boys scanned at any time in pregnancy tended toward lower grades than unscanned boys, but the differences weren’t significant (Stålberg and colleagues, 2009).
• Autism. In the Perth trial, autism was diagnosed in 9 of 1,125 children (0.8%) in the one-scan group and 7 of 1,167 (0.6%) in the five-scan group, not a significant difference (Stoch and colleagues, 2012). A 2018 case-control study at Boston Medical Center compared 107 children with autism, 104 with other delays and 209 developing typically, born from 2006 to 2014. Scan numbers didn’t differ. Against typically developing children, the autism group had slightly deeper scanning but shorter scanning time in the first two trimesters; against children with other delays, deeper scanning in the first. The authors called for research on whether other aspects of exposure “also have adverse effects” (Rosman and colleagues). ISUOG’s safety committee said depth isn’t a measure of exposure, and the paper “does not suggest that ultrasound exposure is associated with ASD” (ISUOG, 2018).

Two reviews pooled the evidence. One, for the World Health Organization, covered 61 publications from 41 studies and concluded that “according to the available evidence, exposure to diagnostic ultrasonography during pregnancy appears to be safe” (Torloni and colleagues, 2009). A 2015 Cochrane review of routine scans before 24 weeks, in 11 trials with 37,505 women, said follow-up “does not indicate that scans have a detrimental effect on children’s physical or cognitive development.” Its summary doesn’t say how many children were followed (Whitworth and colleagues).

What the studies can’t tell you

• How today’s machines compare. The AIUM says the evidence “is based primarily on exposure conditions existing prior to 1992,” the year output limits for pregnancy scans “were substantially increased” (AIUM).
• What keepsake sessions do. The trials compared schedules of medical scans, not long or repeated keepsake sessions.
• Whether small effects exist. “Some older studies have reported effects” such as low birth weight, delayed speech, dyslexia and non-right-handedness, the AIUM says, and “other more recent studies have not demonstrated such effects.” And the absence of definitive evidence, it says, “does not preclude the possibility of adverse effects.”
• What animal findings mean. At Yale, in over 335 mice exposed before birth, ultrasound “for a total of 30 min or longer” while brain cells migrated left “a small but statistically significant number” out of place, more with longer exposure. The authors called for primate studies and “continued scrutiny of unnecessarily long prenatal ultrasound exposure” (Ang and colleagues, 2006).

Doppler, heartbeat recordings and home Dopplers

Doppler tracks movement, such as blood flow (RadiologyInfo.org), and the FDA lists “Doppler fetal heart rate monitors” for listening to the heartbeat. Pulsed and color Doppler put out more energy than the ordinary picture. The AIUM says pulsed Doppler “should not be used routinely due to increased acoustic output,” and ISUOG says that “compared with grayscale imaging, color Doppler increases the total power emitted” (AIUM, ISUOG, 2021).

For the heart rate, the AIUM says “Doppler instruments without imaging capability are permissible to be used,” but spectral Doppler imaging “should not be used to document the fetal heart rate unless clinically indicated.” It recommends an M-mode or B-mode scan instead, “keeping the TI as low as possible, preferably less than or equal to 0.7, and not prolonging the procedure beyond what is necessary to obtain the measurement.” This advice isn’t limited to early pregnancy: it gives index settings for scans before and after 10 weeks (AIUM).

A keepsake heartbeat recording has no medical purpose, and the AIUM “strongly discourages the nonmedical use of ultrasound.” Whether to have one is a reasonable thing to ask your doctor or midwife about. Seeing the heartbeat versus hearing it.

Home Dopplers

Heartbeat monitors sold over the counter, sometimes called doptones, are for professionals, the FDA says: they “should only be used by trained health care providers when medically necessary.” In untrained hands, they could expose a baby to “prolonged and unsafe energy levels,” or give readings that are misread (FDA). The NHS in England says not to use a home Doppler to check the heartbeat yourself. It’s “not a reliable way to check your baby’s health,” and “even if you hear a heartbeat, this does not mean your baby is well” (NHS).

If your baby moves less than usual, or the pattern changes, call your doctor or midwife right away, even in the middle of the night. In England, the NHS says to call your midwife or maternity unit immediately, without waiting until the next day (NHS).

How to keep exposure low at any scan

The AIUM puts the job on whoever holds the probe: “limiting exposure and dwell times,” “monitoring the output display indices,” and using Doppler “appropriately only for a medical indication” (AIUM). You can help:

• Keep every medical scan, and ask for pictures there. The FDA calls keepsake images “reasonable” from a medically indicated exam with no extra exposure.
• Ask who will scan you. The AIUM wants fetal scans done by “appropriately trained and credentialed medical professionals” (questions to ask a studio).
• Ask what the TI reads. The U.S. guideline sets 0.7 or less for pregnancy scans.
• Leave Doppler to medical scans. The AIUM wants it used only for a medical reason.
• Postpone if you have a fever, and tell your doctor or midwife. In pregnancy, a high temperature “can be a sign of an infection,” the NHS says (NHS). With a fever, the AIUM says, scan only if clinically indicated, and wait until your temperature is normal if possible (AIUM).
• Don’t count on a safe number of scans. None of these bodies gives one. If you’re weighing another keepsake session, ask your doctor or midwife.

Where this leaves a keepsake studio like ours

All of this applies to our own sessions: mybaby4D is an elective keepsake studio in Glendale, Los Angeles County. The FDA and the AIUM discourage scans done only for keepsakes. We won’t tell you the experts are wrong, and Safety, in plain words explains how we work with that in mind.

Sessions are as short as a clear view allows: we scan for the pictures, and no longer. When a session is particularly difficult, we take extra time, and we bring you back for another try. That is part of our promise. Whether it’s right for you is your decision. We don’t screen or diagnose. The one number you’ll hear from us is the heart rate at a gender scan, and what it means is a question for your doctor or midwife.

Our 4D Bonding session runs from 16 to 40 weeks. If you want one visit and you want the face, aim for 28 to 34 weeks (choosing your week). It doesn’t check your baby’s anatomy, growth or health: come for the joy of it, not for a health benefit. Whether to have a keepsake scan is your decision, and a reasonable thing to ask your doctor or midwife about.

With a due date, the planner can show which sessions fit your week and which come later. What you enter never leaves this device.

Questions