Ultrasounds: Are they safe?

During my first pregnancy, I received five ultrasounds. Not one of them was “recreational”; I did not pay to get a 3D ultrasound. I was happy each time an ultrasound was done though, to get a chance to have a peek into my baby’s life in the womb. I probably would have gotten a 3D ultrasound if I had the money. I figured that they do ultrasounds on pretty much every pregnant woman so surely I would have heard if there was anything dangerous – surely they wouldn’t do it on everyone if there was any danger, right? I did come across a study that stated that women who received 5 or more ultrasounds during the pregnancy were more likely to have a low birth weight baby. I figured that women having problem pregnancies were both more likely to have more ultrasounds and more likely to have smaller babies already and that, although there was a correlation, there was not a cause-effect relationship between the two. Besides, I thought, what’s wrong with having a small baby? I was far more concerned about having a big baby as both Hubby and I were big. I think Hubby was almost 9 lbs and I was over 10 lbs. (I later learned what the risks of a baby having a low birthweight are, but I won’t get into that right now.)

I had three ultrasounds during my second pregnancy. I received my prenatal care from midwives and it was a much more straight-forward pregnancy than my first. I was a little hesitant but my primary midwife assured me that it was safe, so I didn’t turn down any offered ultrasounds. The first was a dating ultrasound. I was eager to get this one as I’d had 4 consecutive miscarriages and wanted to see that heartbeat. We waited on this one until we could do the triple screen to test for congenital defects as well. The second was the mid-pregnancy scan, when we learned we were having a second healthy baby boy.

The last one was to check his size as I was measuring small. I told her that I measured small the first time and I have a small build anyways, but she said that I had to have the ultrasound so that she could continue to be my midwife – otherwise she’d have to transfer care to an OB as there was concern about Intrauterine Growth Restriction (IUGR). I was not happy about this. My belly was growing every week – it just wasn’t the cm per week that they want to see. I think I was 30 cm at 32 weeks and so on. I was also gaining weight every week so I did not see the need for an ultrasound. I was close to my due date and was concerned about being told that my baby was very big (despite the fact that I was measuring small, I knew that he was not small). I did not want that affecting my mental state as I birthed him, and I did not want pressure to induce if he ended up looking big on the ultrasound. Still, the alternative being transferring to OB care (where s/he would almost certainly require an ultrasound anyways), I agreed. It ended up being a very quick ultrasound (about 5 minutes). The technician asked how much my first son had been. I said “7 pounds, 9 ounces.” She said this baby would be about the same size. Phew. (She was off by more than a pound, as very often is the case. My secondborn was 8 lbs, 13 oz.)

I’m currently pregnant with our third child. I got an early one because we were not completely sure of the dating and we will be getting the 18-20 week ultrasound again this time.

Baby is that tiny blob on the right.

What is Ultrasound?

Ultrasound uses very high frequency sound waves which bounce off of the baby and back to the ultrasound wand. The computer interprets these results and draws a picture. 3-D or 4-D ultrasound takes a series of 2-D images of the baby and the computer compiles them together to make a 3-D image. Time is the fourth dimension in 4-D ultrasound.

What is it used for?

There are many things that ultrasounds are used for during pregnancy.

• Early ultrasounds are pretty accurate at estimated gestational age, give or take a few days. Dating accuracy decreases as the pregnancy continues (later ultrasounds are not as good an indicator of gestational age).
• Ultrasound can detect the baby’s heartbeat sooner than a Doppler, which can be very reassuring to a newly pregnant mama, especially one with a history of early pregnancy loss. Once the heartbeat is detected, the likelihood of a live birth is 82-98%, depending on the woman’s gestational history.
• Ultrasound is useful for diagnosing many unusual things in a pregnancy, such as:
• ectopic pregnancy (when the fertilized egg does not make it all the way to the uterus and implants in the fallopian tube. This is always life-threatening to the mother if the pregnancy continues and requires immediate removal of the fetus and sometimes the fallopian tube, depending on how much damage has been done.)
• molar pregnancy (when the fetus does not develop normally – it grows into a random mass of cells instead of a baby.)
• slow growth of the baby. This is done by comparing the results of an earlier ultrasound to a later one. Keep in mind that this is subject to human error as it is the ultrasound technician controlling where the computer starts and stops measuring the baby’s bones. Still, if there is a large difference between how the baby should be measuring and how it is measuring, it could be cause for concern.
• fetal malformation. This can include some forms of dwarfism, spina bifida, cleft lip and/or palate, and problems with internal organs (heart defects, lung issues, bowel imperfections, etc.). It can also detect some clues that may suggest chromosomal abnormalities such as Down syndrome. It cannot diagnose these, however. Further testing, such as amniocentesis, is required for a diagnosis.
• Ultrasound is used during diagnostic procedures such as amniocentesis and chorionic villus sampling to verify position of the baby and the needle to try to make sure not to stick the baby with the needle.
• Placental location can be determined with ultrasound. The concern is usually placenta previa, which is when the placenta partially or completely covers the cervix. This necessitates a cesarean and can be life-threatening to the motherchild if normal labour is allowed to progress. As the cervix opens, the placenta detaches and can cause severe vaginal bleeding. If the placenta is only low-lying (close to but not covering the cervix) then it might migrate away and not pose any problem. Placenta previa is uncommon and is associated with scars in the uterus (mostly from a previous cesarean, abortion, or removal or uterine fibroids), a large placenta (such as with multiples), or an abnormally shaped uterus. It is almost always diagnosed before the end of the pregnancy.
• Ultrasound can pick up multiple babies and watch for problems such as twin-to-twin transfusion.
• Too much or too little amniotic fluid can be detected on ultrasound. Either condition can negatively affect the baby.
• 3-D ultrasound is better at picking up smaller defects than 2-D ultrasound and, when done for medical purposes, can be done quicker than 2-D (thus lowering exposure) as it takes more images at once, which can later be dissected on the computer to get the needed images. “It took a mean time of 1.1 minutes to obtain the 3D volumes…With the standard 2D technique, the structural surveys were done in a mean time of 13.9 minutes”.

What could interfere with ultrasound?

Maternal obesity can make it difficult to get a clear image, especially with 3-D imaging or if it is very early in the pregnancy. If it is very early then a transvaginal scan may be performed instead of an abdominal ultrasound. The technician may have to turn up the intensity of the ultrasound in order to get through layers of fat on an obese mother.

Low amniotic fluid can make it difficult to get a clear image as well. Doubling your water intake for a few days before the ultrasound can ensure that the amniotic fluid levels are at a good level to get a clear image (most pregnant mothers need to drink more water than they currently are anyways).

When are ultrasounds performed?

1. A first ultrasound is sometimes done early in the pregnancy to confirm the pregnancy and estimate gestational age. Ultrasound can pick up the gestational sac as early as 4.5 weeks, the yolk sac from about 5 weeks, and the embryo from around 5.5 weeks.
2. If the mother opts for prenatal testing for congenital defects (called the triple or quad screen), then an ultrasound will be performed between 11 and 13 weeks. 5% of women who do this test will receive a false positive for Down syndrome. This means that for 1 out of 20 women who get this screening test, the ultrasound will show a high risk of having a baby with Down syndrome when, in fact, the baby does not have it. Around 90% of couples expecting a child diagnosed with Down syndrome prenatally will choose to end the pregnancy so accuracy is extremely important. A positive screening result is usually followed with amniocentesis (after 15 weeks) which is 98-99% accurate; however, it comes with a 1 in 200 risk of miscarriage. If you know that you would choose to continue the pregnancy if you received a positive result, then you may not want to risk it.
3. A second trimester scan is done between 18 and 20 weeks. This is the most commonly performed scan. This is mostly to check for congenital malformations, multiple pregnancies, placental position, and fetal growth. If the parent(s) would like to know the gender and the baby cooperates, then it can often be detected at this ultrasound.
4. A scan may be done towards the very end of the pregnancy to check the baby’s positioning if there are concerns about a transverse or breech lie, assess fetal growth, and verify placental position.
5. Parent(s) may choose to get a 3-D or 4-D ultrasound as a “keepsake”. Most of the time they must pay out-of-pocket for these as they are not prescribed by a doctor. Some places offer a series of up to 6 ultrasounds over the course of the pregnancy.
6. A scan may be done at any time if there are concerns about the baby or the pregnancy. This may be indicated by premature spontaneous rupture of membranes (amniotic sac breaking before 37 weeks gestation), unexplained vaginal bleeding, abnormal (increased or decreased) fetal movements, or some other circumstances.

Is it safe?

The short answer is that we don’t know. Low birth weights, speech and hearing problems, brain damage, and left-handedness (thought to sometimes be an indicator of brain damage) have been reported by small studies but have not been confirmed by larger studies. Some abnormalities have been observed in studies using animals, but this hasn’t been seen in studies with humans. I can’t word it better than I see here, so I will just cut and paste what is written.

Equipment Choice can make a difference 

In general, practitioners of fetal ultrasound operate on a Titanic Mentality:  Safety is assured, therefore precautions are unnecessary.  I would be happy to be proven wrong.  Tina Ureten, the operator of a chain of commercial entertainment/bonding fetal ultrasound facilities in Canada (UC Baby), made this point in a spirited response to criticism in the Aug 26, 2003 edition of The Medical Post (Canada): “Ultrasound has been used extensively by Canadian doctors and health practitioners for more than 40 years without any concern.”  This background of indifference has caused difficulties for me in trying to have output intensities given serious weighting in the tendering and selection process for new equipment.  Vendors repeatedly tell me that they have not previously been asked for this information, and without precedent or support from the wider user community it is hard for someone in a small facility to insist on treating acoustic outputs as a priority in the purchase process. 

Equipment choice can make a difference. The General Electric Logiq 9 provides satisfactory fetal imaging for most circumstances with a default Mechanical Index (MI – described in section 3) of about 0.2 using its fundamental frequency.   A recent report (4) gives an MI value of about 1 for second-trimester fetal imaging with the equipment that the authors were using (Philips HDI 5000), which is a similar value to our Toshiba Aplio. While it is not possible to know how much of the rise in acoustic intensities over time was really necessary for essential image improvements and also to satisfy increased penetration requirements in our increasingly obese populations, I have not seen a 1000-fold increase in image quality since 1980. (Anna: emphasis mine)  Comparison with mammography, where there has been intense consumer-driven demand for dose reduction and image improvements, is instructive:  “Standardization of mammography led to a decrease in mean glandular dose from 14 to 1.8 mGy with concurrent improvement in image quality” (5).

Specialized diagnostic ultrasound has been shown to have a therapeutic role in some stroke situations by helping thrombolytic treatment for blood clots involving the middle cerebral artery; this made the grade to publication in the New England Journal of Medicine (13) with commentary and mechanism speculation (14).  The device was different from those used in fetal scanning, there was a deplorable absence of ultrasound intensity measurements/calculations and the duration of exposure was beyond most fetal situations, but the point remains that ultrasound exposure in the diagnostic range of intensities can have demonstrable biological effects.

Unintended Adverse Consequences

Perhaps the most interesting example of unintended adverse consequences in obstetrics is the history of the use of diethylstilbestrol (DES) (18, 19). 

Reference 18 is a Centers for Disease Control (CDC) summary with relevant links.  The drug was prescribed to prevent miscarriages; although it was shown to be ineffective in 1953 it continued to be used until the unusual complication of clear cell adenocarcinoma of the vagina in some of the daughters of women who had taken the drug in pregnancy was recognized in 1971.  If this distinctive adverse effect had not occurred when, if ever, would the increase in more commonplace problems of infertility and complications of pregnancy in women who had been exposed as fetuses have been recognized?  A reliable source tells me that she heard a radio interview some years ago in which it was mentioned that the first recognition of the DES-carcinoma of the vagina association was by a group of mothers of affected daughters conversing in an elevator and not by the preceding medical investigational interviews.

Reference 19 has an ad from 1957 recommending one brand of DES for all pregnancies.

A disturbing consequence of the ability to identify fetal gender has been termination of female fetuses in some societies; it has been estimated that up to 10 million female fetuses have been aborted in India in the last 20 years (30).

There is far more information on this website, I encourage you to read all of it.

One big risk (possibly the biggest) is over- or under- diagnosis by poorly trained technicians and/or poor equipment. The emotional strain on a pregnant mom who has received a positive screening test and is waiting for more conclusive results is huge. A couple may make the difficult decision to end the pregnancy if a poor outcome is predicted only to discover afterwards that their baby had been misdiagnosed or they may be told that their baby is fine and then be unprepared when they discover their child has special needs when s/he is born. Keep in mind that ultrasound and other diagnostic tests are not perfect and there is no way to ensure that every extraordinary circumstance is discovered before the birth. There will still be babies born with previously undiagnosed birth defects, the location of the placenta cannot always be determined, and surprise twins even pop up occasionally.

Even as a mom who did not receive a positive screening, but was just waiting to get the results back, it put a lot of stress on me. With my first, I didn’t hesitate to get the screening. With my second, I hesitated but got it. With my current pregnancy, we decided not to do the screening. I would choose to continue the pregnancy so I am okay with waiting until the mid-pregnancy ultrasound when they will check for markers of any defects just so that we can be prepared when the baby is born. The mid-pregnancy ultrasound is very important to us, personally, because we are preparing for our second homebirth. We want to make sure that the placenta location is good, how many babies we are having, and if there are any issues that the baby may have that would make it better for him/her to be born in a hospital.

For those of you that put a lot of stock in the recommendations of government organizations, here they are:

From the FDA:

Ultrasound Equipment Used in Making Prenatal Videos for Entertainment

The Food and Drug Administration (FDA) has become aware of several enterprises in the U.S. that are commercializing ultrasonic imaging of fetuses by making "keepsake" videos. We are concerned about this misuse of diagnostic ultrasound equipment

From a medical standpoint, ultrasonic fetal scanning is generally considered safe, and should be used without hesitation when clinical benefit is expected. But ultrasound energy delivered to the fetus cannot be regarded as innocuous. Viewed in this light, exposing the fetus to ultrasound with no anticipation of medical benefit is not justified. Thus, we believe that these prenatal entertainment videos should not be performed.

Persons who promote, sell or lease ultrasound equipment for making "keepsake" fetal videos should know that we view this as an unapproved use of a medical device, and that we are prepared to take regulatory action against those who engage in such misuse of medical equipment.

From Health Canada:

Concern about Fetal Ultrasound for Keepsake Videos

In all instances, the risks of fetal ultrasound will depend on the ultrasound levels and duration of exposure. The ultrasound level is now displayed on the monitor, and this lets qualified operators assess the potential for damaging the fetus. Risks can be minimized by keeping the ultrasound level and exposure time as low as possible without losing the information needed for diagnosis.

When fetal ultrasound is done for a keepsake video, no medical information is provided to justify exposing the baby to ultrasound.

Health Canada recommends that you have fetal ultrasound only on referral from a licenced health care provider.

Health Canada's Role

Health Canada regulates diagnostic ultrasound devices under the Food and Drugs Act, the Radiation Emitting Devices Act, and the Medical Devices Regulations. This ensures the safety and effectiveness of the devices when they are used for their licenced diagnostic purposes and according to guidelines for safe use.

Health Canada has established Guidelines for the Safe Use of Diagnostic Ultrasound. The Guidelines state that ultrasound should not be used for any of the following activities:

• to have a picture of the fetus, solely for non-medical reasons
• to learn the sex of the fetus, solely for non-medical reasons
• for commercial purposes, such as trade shows or producing pictures or videos of the fetus

Health Canada is also working with the Society of Obstetricians and Gynecologists of Canada (SOGC) to develop a user-friendly clinical practice guideline on the safety of obstetric ultrasound.

UK Department of Health has stated similar concerns here (It’s very long and won’t allow me to copy and paste. Scroll down to pages 64-65).

I have not been able to find any statements about ultrasound from Australia’s Department of Health and Ageing.

The general verdict is that, because we don’t really know what dangers there are, to limit ultrasounds only to those which are medically indicated – just as you wouldn’t take a drug that had unknown effects during pregnancy unless it was absolutely necessary. The current trend towards “recreational” ultrasounds for the sole purpose of a picture for the baby book or to learn the baby’s gender is disturbing. Some parents have even purchased 3-D machines in order to be able to see the baby whenever they want. “Keepsake” 3-D ultrasound booths in malls have been banned. We don’t know for certain that it is 100% safe so why risk your baby’s safety when there is no medical indication to do so? Is it really worth possibly risking your child’s health by getting unnecessary ultrasounds just for that picture for the baby book or so you can pick the colour of the nursery walls?

My personal exception to that would be if my baby was diagnosed with something that would make life outside the womb impossible, then I would likely get at least one 3-D or 4-D ultrasound session, if not more, in order to be able to see the child while s/he is alive and more fully enjoy our short time together. I have heard that there are even some companies that provide this free of charge in this circumstance.

Keep in mind that dopplers use ultrasound technology to detect the baby’s heartbeat. You may want to consider asking your doctor or midwife to use a fetoscope or pinard horn instead of the Doppler for prenatal visits and request intermittent vs. continuous fetal monitoring during labour (side note: intermittent monitoring is proven just as safe as continuous monitoring. Continuous monitoring increases rates of interventions without a corresponding bettering of fetal outcomes.)