Missed miscarriage is also called silent abortion or silent miscarriage.
Silent miscarriage can only be determined by ultrasound, because bleeding or abdominal cramps, which may indicate a possible miscarriage, are not present. Before a diagnosis is performed by ultrasound, multiple tests take place. In case of missed abortion, fetal heart activities and child movements are not found. The embryo has not been able to develop further. The unborn fetus is therefore not viable.
Falling levels of pregnancy hormone HCG, which sustains pregnancy, may be the cause.
From angelababy In Q&A