Will There Be A Miscarriage If There Is No Heart Beat?

i am 6weeks 4days pregnant through ivf, i was told to stop taking my progestorone and estradol because the sac is low lying and there is no heartbeat< today is monday and i stopped everything on saturday and due for an ultrasound on friday, i was told to expect a miscarriage, is this true and the fetal pole and crown rump measures well in size