I had an emergency scan and only saw the sac no fetus what does this mean?

Gestational sac: If you had an ultrasound with only a gestational sac, it could be either a very early pregnancy or what is called a missed abortion. If you are only 4-6 weeks you may not see a fetus, but if you are further along like 10 weeks it may be a missed abortion. That term simply means a pregnancy where there is no fetus and just placenta tissue.