We’ve all seen the pregnancy announcements with the grainy black-and-white first “picture” of baby held by excited parents-to-be. Most women are offered at minimum an ultrasound at 7 or 8 weeks pregnant for dating purposes, the 20-week anatomy scan, and a late pregnancy ultrasound to make sure “everything is going ok.”
When I told my OB during my first pregnancy that I didn’t want to do the 7-week ultrasound, she looked at me like I was insane.
Ultrasounds are so common today that their safety and necessity are rarely questioned even though their appearance on the birth scene is relatively recent.
The rise in ultrasound Usage
Ultrasounds came into use in obstetrics around the mid-1950s in Glasgow, became popular in British hospitals in the 1970s, and they have since become a standard part of prenatal care in the US since the late 1970s.
The technology came from an instrument used to detect flaws in old ships that an obstetrician and engineer adapted for the use we see today.
How does it work?
That blurry image isn’t a picture of your baby per se.
When the wand is placed on your belly (or into your vagina if it’s a transvaginal ultrasound), high-frequency sound waves – “ultrasonic” waves which are above the audible range of our human hearing – are projected.
The image we see on the screen or printed out is the reflection of those sound waves bouncing off of baby, the echoes of the waves.
Are they safe?
"Although there is a lack of evidence of any harm due to ultrasound imaging and heartbeat monitors, prudent use of these devices by trained health care providers is important," says Shahram Vaezy, Ph.D., an FDA biomedical engineer. "Ultrasound can heat tissues slightly, and in some cases, it can also produce very small bubbles (cavitation) in some tissues." The long-term effects of tissue heating and cavitation are not known. Therefore, ultrasound scans should be done only when there is a medical need, based on a prescription, and performed by appropriately-trained operators.
The safety of ultrasounds – both the technology and the use of the test – is a big debate, though not one discussed in typical prenatal care settings. Most medical professionals believe it to be safe and see no noticeable pattern of side effects.
Regarding the ultrasound technology itself, the question of safety remains.
ACOG recommends that they be used sparingly and only for medical purposes: “Currently, there is no reliable evidence that ultrasound is harmful to a developing fetus. No links have been found between ultrasound and birth defects, childhood cancer, or developmental problems later in life. However, it is possible that effects could be identified in the future. For this reason, it is recommended that ultrasound exams be performed only for medical reasons by qualified health care providers.”
Regardless of its ubiquitous use, there are some concerns about its impact on baby.
One common concern is about the temperature changes the ultrasound waves can cause on the baby’s developing organs and body. Increasing tissue temperature by 1.8-2.7 degrees Fahrenheit is considered safe, but studies have shown both doppler and ultrasounds may heat tissue above that, especially when the wand is stationary for multiple seconds.
Doppler ultrasound which uses continuous waves rather than the traditional pulsing waves has shown significant tissue heating.
Animal studies show a pretty clear connection between brain hemorrhages, decreased cell division, and ultrasound exposure.
The human studies are more rare, but there are quite a few to highlight – one showing a correlation between first trimester ultrasounds and severity of symptoms in autistic boys, one showing a small link between fetal death and one routine ultrasound at 16-20 weeks, and a collection connecting ultrasounds to increased incidences of Autism, ADHD, jaundice, childhood cancers, and allergies.
The research is interesting to dig into, though the confounding variables and time between ultrasound exposure and potential related effects make it challenging to prove a definitive connection.
The more you look into the research, the more clear it is that safety has not been proven, mostly just assumed.
Another big issue is misdiagnoses that can come from an ultrasound. It’s not a perfect technology, and there’s always room for human error in the analysis of results. When care is then dictated based on the results of the ultrasound, we can see a domino effect of the intervention. Some pregnancies are even terminated based upon ultrasound findings.
An early ultrasound, for example, can misdate the gestational age. When mama gets to the end of her pregnancy, she may be encouraged to induce for being “overdue” when in reality her date was just wrong.
Something like placenta previa may be diagnosed in an early ultrasound, leading to stress in mama and repeat ultrasounds with increased exposure, when a condition like that typically resolves itself throughout the pregnancy with no intervention necessary (one study up to 98% of women diagnosed with placenta previa no longer had the condition by delivery).
Another common risk is in late pregnancy ultrasounds when “your baby is too big” or “your baby is too small” or “your fluid is low” are all used to encourage induction. Late-term ultrasounds are notoriously inaccurate, and often the diagnoses turn out to be false. The “big baby” is born at 6 pounds.
Knowing an estimated fetal weight increases the risk of having a c-section in one study. Ultrasounds can be up to two pounds off which makes them a pretty unreliable way to predict baby’s birth weight!
Even if the “only risk” is repeat ultrasounds, it’s a risk to consider.
What are the benefits? Are there alternatives?
Studies show there is no improved fetal outcomes with the use of diagnostic ultrasounds (the conclusion of this study states: “Routine ultrasound scanning does not improve the outcome of pregnancy in terms of an increased number of live births or of reduced perinatal morbidity. Routine ultrasound scanning may be effective and useful as a screening for malformation. Its use for this purpose, however, should be made explicit and take into account the risk of false positive diagnosis in addition to ethical issues.”)
There are definitely a few benefits ultrasounds can provide, though a lot of the benefits can be found through other methods.
One main advantage talked about in the medical field is that they are considered to be non-invasive. While this is true in a sense, it partly depends on what kind.
A transvaginal ultrasound is performed by inserting a wand into the vaginal canal, something most would deem invasive. As with any vaginal exam or procedure, this carries a risk of infection.
Considering the risks outlined above of increased tissue temperatures, the “non-invasive” identifier may also be off.
An ultrasound before 14 weeks has been shown to give the most accurate due dating, though other studies have shown that mamas with regular menstrual cycles can have just as accurate dating from the date of her last menstrual period. But for mamas with irregular cycles or who don’t track closely, an ultrasound can provide a decent estimate of gestational age.
A common use of ultrasound is to find out the sex of the baby. This can also be done with blood tests, even at-home blood tests so you don’t have to go to an office for a draw.
An ultrasound can help confirm a multiples pregnancy. A practitioner may also be able to confirm this through palpating mama’s belly, but an ultrasound can give answers about what type of twins (or more!) mama is carrying and if there are any health issues to be aware of moving forward in the pregnancy.
Ultrasounds can help with diagnosing issues like an ectopic pregnancy or placenta previa. The anatomy scan can reveal certain development issues with baby’s organs and limbs.
Bottom line: do I need to get an ultrasound?
At the end of the day, the call to get any ultrasound while pregnant is mama’s choice. Some feel comfortable going through pregnancy with zero. Some feel the need to get every offered ultrasound and then some extras as well.
There’s something exciting about seeing your baby, I get it!! And there are times when there is definitely a medical need to get an inside look.
I personally chose to get one – the anatomy scan – each pregnancy. With my second pregnancy, I decided to get a second at 41 weeks to check in. In retrospect, I likely wouldn’t do that 41 week ultrasound again, but at the time, it felt right.
As with everything, there are risks and benefits to the ultrasound technology itself as well as the timing of utilizing this intervention and the dominoes that may fall from the results.