Tiffany C. Brawn

Human embryos may be especially vulnerable to Thermally Induced Teratogenesis, or hyperthermia (overheating). Potentially significant side-effects could occur in highly sensitive neural tissue, cerebral vessels, and in fetal bone in the second and third trimester. Non-thermal effects, including non-ionizing radiation, are indicated by the mechanical index.

… Unfortunately, many of the doctors and sonographers performing fetal ultrasound are not fully aware of the safety parameters, aren’t regularly retrained, or even bother to follow the safety standards set by the AFDA including not allowing the transducer to remain stationary (to get a better picture) or using the technology in the first trimester of pregnancy when the embryo cannot dissipate excess heat.