Its safety and efficacy are still highly questionable. Even the FDA says, "While ultrasound has been around for many years, expectant women and their families need to know that the long-term effects of repeated ultrasound exposures on the fetus are not fully known." http://www.fda.gov/fdac/features/2004/104_images.html
Most studies and authorities recommend that ultrasound is safe only when "medically necessary". The question really comes down to personal practitioner selection: "what warrants medical necessity?" Here is where interpretation is vast and undefined. While ACOG recommends that ultrasound examinations be done for specific reasons, such as a suspected ectopic pregnancy, a possible miscarriage or detection of possible birth defects, many physicians include one examination as part of routine care, at 18 to 20 weeks of pregnancy. The March of Dimes Birth Defects Foundation estimates that 70 percent of American women have at least one ultrasound examination during their pregnancy.
Perhaps a more prudent approach would be to define medical necessity as "life saving" and forgo prenatal ultrasound procedures for less relevant reasons. The original axiom of medicine "first do no harm" should always beconsidered when determining "medical necessity" for ultrasound.
" Lack of risk has been assumed because no adverse effects have been demonstrated clearly in humans. However, other evidence dictates that a hypothetical risk must be presumed with ultrasound. Like-wise, the efficacy of many uses of ultrasound in improving the management and outcome of pregnancy also has been assumed rather than demonstrated, especially its value as a routine screening procedure." http://www.ob-ultrasound.net/joewoo3y.html
In accordance with medical protocol, the safety and efficacy of prenatal ultrasound has not yet been proven via peer reviewed research. On the contrary, current studies are cautioning its use. Prenatal ultrasound, therefore may even be considered, "experimental and investigational". Concerned with nerve system stress, doctors of chiropractic are always on the look out for procedures that may cause more damage than benefit. Now a new study presents data we have suspected all along: ultrasound may affect brain development.