Guidlines and recommendations for safe use of Doppler ultrasound in perinatal applications

Authors:Barnett, S. B. and Maulik, D.
"The risk of inducing thermal effects is greater in the second and third trimesters, when fetal bone is intercepted by the ultrasound beam and significant temperature increase can occur in the fetal brain. Non-thermal bioeffects may be more significant in early gestation, when the relatively loosely tethered embryonic tissues are exposed to an ultrasound beam in a liquid path."