Are prenatal ultrasounds safe?

Question

I recently expressed concern to my midwife about the use of prenatal ultrasounds. She scoffed at the idea that they could do harm and proceeded to use a Doppler device to monitor our baby's heart rate.

After which, we did a bit of digging and found some resources that cast doubt on the idea the ultrasounds are safe and that the use is justifiable.

Would you be able to read the following articles and provide comments as to the validity of the statements? Any additional comments or resources are very much appreciated.

http://www.midwiferytoday.com/articles/ultrasoundrodgers.asp

http://drbenkim.com/articles-ultrasound-pregnancy.html

http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/ucm115357.htm#rb

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1538990/?tool=pmcentrez

Thanks in advance,

Answer 1

Ultrasonic waves cause some heat and vibration, so prolonged exposure can theoretically have a negative impact.

The last article you cite shows 30 minutes of exposure in fetal mice can mildly disrupt their neuronal development. Rat neuronal development occurs much more rapidly than human development. The rat's gestational period is about 23 days, compared with around 260 for humans, so disrupting it in significant ways is easier to do with relatively short exposures. In other words, 30 minutes of rat gestational time is roughly equivalent to 300 minutes of human gestational time. Using doppler to measure heart rate, and even the typical one-off 19-week fetal scan to check for abnormalities and determine the sex of the fetus, does not take anywhere near this amount of time.

The FDA article mentions that the exposure is not particularly harmful, but as with any radiation exposure, it should be used sparingly.

The other two articles are not particularly reputable. As with anything, there will always be risks. You probably shouldn't have weekly hour-long sonograms, but a one-minute doppler scan carries such a low risk that personally, I would consider taking a hot shower and driving on a bumpy road to be riskier.

Answer 2

There is a long story about this topic, going back to its first introduction in the 1950s. It probably doesn't help that you can crank up the power on an ultrasonic device to do things like break up kidney stones; surely, such technology must come with tradeoffs, like X-rays do.

A large, longitudinal study reported in 1993 with 15,151 pregnant mothers as subjects found that:

The mean numbers of sonograms obtained per woman in the ultrasound-screening and control groups were 2.2 and 0.6, respectively. The rate of adverse perinatal outcome was 5.0 percent among the infants of the women in the ultrasound-screening group and 4.9 percent among the infants of the women in the control group (relative risk, 1.0; 95 percent confidence interval, 0.9 to 1.2; P = 0.85). The rates of preterm delivery and the distribution of birth weights were nearly identical in the two groups. The ultrasonographic detection of congenital anomalies had no effect on perinatal outcome. There were no significant differences between the groups in perinatal outcome in the subgroups of women with post-date pregnancies, multiple-gestation pregnancies, or infants who were small for gestational age.

They did define 'adverse perinatal outcome' as:

Adverse perinatal outcome was defined as fetal death, neonatal death, or neonatal morbidity such as intraventricular hemorrhage.

Which may be a bit more... lethal than you're looking for. It's very tricky to judge the results of these kinds of pediatric surveys on effects such as obesity, increased or decreased intelligence, etc, because so many other confounding factors are present. As such, at least for this study, the binary approach of 'dead' or 'not dead' shows that there's no increased risk of really, really bad outcomes as a result of ultrasounds. And that's using late 1980s-early 1990's imaging tech.

As such, in 2002, Marinac-Dabic et al called for a more inclusive definition of 'adverse outcomes':

However, there have been some reports that there may be a relation between prenatal ultrasound exposure and adverse outcome. Some of the reported effects include growth restriction, delayed speech, dyslexia, and non-right-handedness associated with ultrasound exposure. Continued research is needed to evaluate the potential adverse effects of ultrasound exposure during pregnancy.

I tend not to think that left-handedness is as bad as dyslexia or growth restriction, given that Presidents of the United States tend to be either right or left handed, but the other charges are definitely worth investigating.

As such, in 2009, the WHO published a meta-analysis of the literature to determine if there were any adverse effects for the practice. They concluded:

Ultrasonography in pregnancy was not associated with adverse maternal or perinatal outcome, impaired physical or neurological development, increased risk for malignancy in childhood, subnormal intellectual performance or mental diseases. According to the available clinical trials, there was a weak association between exposure to ultrasonography and non-right handedness in boys (odds ratio 1.26; 95% CI, 1.03–1.54).

tl;dr: In effect, by the best judgement we have, ultrasonic imaging is a safe screening method, and has no adverse effects on the baby.

Answer 3

There is some minor concern that ultrasounds could have medical effects on the fetus. However, if this is true then the effect is very slight... any strong correlations would have been discovered by now, decades later.

Considering that they're not just a way for parents to see their baby before birth, but important diagnostic tools that allow doctors and other medical personnel to avoid potentially life-threatening conditions (for both mother and baby) they're more than safe. It's actually unsafe not to use them (as directed by a doctor). The benefit certainly outweighs any risk they may pose.