There are also questions about whether
it matters that apoptotic activity in the fetal liver is raised
transiently, and there is some difficulty in explaining the
mechanisms of damage (whether due to thermal or non thermal effects).However, recent research
has advocated Doppler measurement of the cardiac and
infracardiac regions of the 11 to 13 + 6-week fetus5,6.There are, however, two other recent
animal studies which have demonstrated a relationship
between length of exposure to Doppler ultrasound and
potentially irreversible biological effects3,4.