The study of vibrational effects is ongoing, relevant and significant. Below is an excerpt from an excellent discussion of ultrasound exams for pregnant women. It covers many aspects of the issue. In particular, below, it discusses some of the dangers.
"Studies on humans exposed to ultrasound have shown that possible adverse effects include premature ovulation, preterm labour or miscarriage, low birth weight, poorer condition at birth, perinatal death, dyslexia, delayed speech development, and less right-handedness. Non right-handedness is, in other circumstances, seen as a marker of damage to the developing brain. One Australian study showed that babies exposed to 5 or more doppler ultrasounds were 30% more likely to develop intrauterine growth retardation (IUGR)- a condition that ultrasound is often used to detect."