What Causes Sudden Loss Of Fetal Movement During Pregnancy?

Hi, i just received a message from my officemate, the ultrasound result is "Within the enlarged uterusis a single fetus in cephalic presentation at the time of examination. Real time scans reveal absence of fetal movements and cardiac activity" she said she will be operated this afternoon and the baby is gone. 3 days ago she told us she felt the movement of her baby. How come that her baby is gone.