Belly Basics: Ultrasound

What is an ultrasound?

Obstetric ultrasound is the use of sound waves (sonar) to get a picture of the inside of the uterus.  It can be used to date a pregnancy, determine the sex of the fetus, reveal a multiple pregnancy, and detect abnormalities or potential complications.  It was first used in the 1950s, shortly after a study revealed an increased rate of cancer among children whose mothers were given x-rays during pregnancy (this was a common procedure to measure the birth canal.  It increased in popularity during the 1970s, and by the 1980s was routine in many countries. [1]

What is the current practice?

In the US, it is estimated that 70% of women receive at least one ultrasound during their pregnancy. [2]

What does the evidence suggest concerning routine ultrasound?

Routine ultrasound can help doctors determine a due date, predict the weight and sex of the fetus, as well as detect multiple pregnancies, birth defects, and possible complications (such as IUGR and placenta previa).   However, the actual medical benefit of routine ultrasound for many of these purposes has been challenged through research.  [3]

For example, the for the diagnosis of birth defects and possible complications, ultrasound consistently has a high false positive rate, meaning that many fetuses and mothers are diagnosed with problems that don’t actually exist. [4] In many cases, palpation of the uterus has been shown to be at least equally effective at diagnosing IUGR, although even with a diagnosis there is still no effective treatment for IUGR. [5]

“Pregnant women often automatically assume that antenatal detection of serious problems in the baby means that lives will be saved or illness reduced. Knowing about the problem in advance did not benefit these babies; more of them died. They got delivered sooner, when they were smaller, a choice that could have long-term effects. All twelve babies with abdominal wall defects survived. But for the six detected on the scan, their length of hospital stay was longer and they spent longer on ventilators, though the numbers are too small to be significant. They were operated on sooner (four hours rather than thirteen hours) but the outcomes were the same.” [6]

Ultrasounds are also notoriously inaccurate when it comes to determining the due date (up to 3 weeks deviation when done in late pregnancy) [7][8] and size of a baby — in some cases more than a pound off of the actual birth weight. [9]

Ultrasound has also demonstrated an increased risk of miscarriage [10], and has even been implicated as a cause for birth defects and autism. [11]  So far it is unknown how the fetus experiences an ultrasound scan.

One of the more theoretical but potentially serious risks of ultrasound is the inconsistent qualifications of the technicians and the current lack of regulations about safe use.  [12]

The safety issue is made more complicated by the problem of exposure conditions. Clearly, any bio-effects that might occur as a result of ultrasound would depend on the dose of ultrasound received by the fetus or woman. But there are no national or international standards for the output characteristics of ultrasound equipment. The result is the shocking situation described in a commentary in the British Journal of Obstetrics and Gynaecology, in which ultrasound machines in use on pregnant women range in output power from extremely high to extremely low, all with equal effect. The commentary reads, “If the machines with the lowest powers have been shown to be diagnostically adequate, how can one possibly justify exposing the patient to a dose 5,000 times greater?” It goes on to urge government guidelines on the output of ultrasound equipment and for legislation making it mandatory for equipment manufacturers to state the output characteristics. As far as is known, this has not yet been done in any country. [13]


Despite the hopes of its inventors and supporters of its use, there is evidence to support the idea that ultrasound does not improve birth outcomes.

“There was no evidence of a significant difference between the screened and control groups for perinatal death. Results do not show that routine scans reduce adverse outcomes for babies or lead to less health service use by mothers and babies.” [14]

As with many other pregnancy interventions, ultrasound is a useful diagnostic tool, but it is unnecessary for it to be used routinely on a large portion of the pregnant population.  Since birth practices (such as induction and c-section) are often based on the babies estimated due date and weight, accuracy of diagnosis is critical to the best birth outcomes for women and babies.  At this time, ultrasound technology is not accurate enough to determine necessary interventions, so either we need to reconsider its widespread use or change our birth practices (or both).

Once upon a time, X-ray was considered a useful diagnostic tool during pregnancy as well, with some doctors even claiming that there were “no danger” as long as the exam was performed by a “competent radiologist.”  Many women received them before it was determined that such exams caused childhood cancers.  [15] Are we making the same hasty mistake with ultrasounds?

“The casual observer might be forgiven for wondering why the medical profession is now involved in the wholesale routine examination of pregnant patients with machines emanating vastly different powers of energy which is not proven to be harmless to obtain information which is not proven to be of any clinical value by operators who are not certified as competent to perform the operations.” [16][17]

Will ultrasound go the way of the x-ray?  In 50 years, will new research reveal the consequences of such cavalier use of this technology?

Final Thoughts

The ultrasound scan shown above is actually mine from my first pregnancy, and before I began my research into ultrasounds, I didn’t give a second thought to whether or not the procedure was actually necessary.  Like many women, I enjoyed seeing my baby every few months on that ultrasound — I found it very reassuring in the beginning of my pregnancy, since I had experienced a loss a few years before.  We even went in for a “4-D” ultrasound to find out the sex of our baby, and that too was a memorable experience.  That said, I don’t think I will get any ultrasounds with my next pregnancy — not because I think they’re dangerous, but because I just think they’re not necessary, and may cause some women undue stress.  Knowing what I know now about the dubious accuracy of such scans, and how those results can lead to unnecessary interventions, leads me to think that most low-risk, healthy pregnant women don’t require them.   So as long as I’m in that category, I’d rather be left in the dark.

Further Reading

To Ultrasound or Not to Ultrasound

Is Ultrasound Scanning During Pregnancy Worth the Risks?

Ultrasound: More Harm than Good?

Ultrasound Scans Cause for Concern

Ultrasound: Weighing the Propaganda Against the Facts

The Dangers of Prenatal Ultrasound


Born in the USA, Wagner (book)

Ina May’s Guide to Childbirth, Gaskin (book)

Midwifery Today


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