Exposure to ultrasound while pregnant may affect brain development in the fetus, suggests a study on mice.

But experts caution that it is too soon to extrapolate the findings to humans. They stress that the imaging technique has overwhelming benefits and pregnant women should not skip essential appointments.

The new research involved using a chemical to trace brain cells in growing mouse embryos. The researchers exposed the embryos to ultrasound shortly afterwards, late in the third week of gestation, a crucial period for mice in which brain cells become organised.

Dissections following the birth of the mice showed that a small percentage of brain cells had not migrated to their normal place. For example, 6% of the chemically tagged brain cells had not migrated normally in mice exposed to two 30-minute ultrasound sessions.


It may be that the ultrasound waves somehow disrupt the connections formed between cells as they move into their proper location, suggests Pasko Rakic at Yale Medical School in New Haven, Connecticut, US, who carried out the research with colleagues.

Still source

Rakic says the brains of these mice still appear healthy to the naked eye. Moreover, his team has not yet tested to see whether the mice have abnormal mental abilities. And he notes that the source of the ultrasound waves remained fixed, which could have increased the risk of disrupting the cells, unlike in the checkups on female patients where medical staff continuously move the ultrasound source.

Doctors generally recommend that women receive two ultrasound checkups during the course of their pregnancy to assess fetal development, each of which can last around 30 minutes. The images generated by the pulses of ultrasonic waves can reveal information about the age of the unborn child, its position in the womb and whether it has any abnormalities.

Some previous studies have suggested that ultrasound may delay speech or cause genetic abnormalities in humans, but experts say these results have not been replicated.

Enlightened era

“At the end of the day, nothing has been reproducible, but it doesn’t mean it couldn’t be,” says Lawrence Platt, director of the Center for Fetal Medicine and Women’s Ultrasound, in Los Angeles, California, US.

“The widespread use of obstetric ultrasound during the past generation has transformed pregnancy from the dark ages to an era of enlightenment,” says Frank Chervenak at the Weill Medical College of Cornell University, New York, US. He says that “it would not be reasonable to extrapolate the new findings in the mouse model to appropriately performed obstetric ultrasound in the clinical setting”.

“I would say that the benefits of the ultrasound for diagnosis are so big that I would not hesitate to use it at all,” Rakic adds.

Trend-setting celebrity

However, experts say that the results warrant further research, especially given the dramatic rise of non-medical “boutique” ultrasounds – which many companies offer in shopping malls to expectant mothers for around $200. It is feared that their popularity may rise still further following reports that expectant celebrities such as Tom Cruise bought home-use ultrasound machines.

The recent explosion in boutique imaging is partly due to the growing sophistication of 3D ultrasounds, which when used in a hospital setting can provide important details to doctors about hard-to detect spinal abnormalities, clubfoot or cleft lip. It is now possible to process the ultrasound information quickly and offer these pictures, and moving footage, on demand. The US Food and Drug Administration has made a strong recommendation against commercial ultrasound movies.

“Mothers leave falsely reassured and then they miss their scheduled ultrasounds with their doctor,” says ultrasound expert Jacques Abramowicz at Rush University Medical Center, Chicago, Illinois, US. He says that this has resulted in some serious birth abnormalities going undetected in the womb.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0605294103)