The sudden absence of fetal heart sounds may be caused by various pathogenic factors such as umbilical cord factors, fetal factors, maternal factors, etc. Fetal death in the uterus requires immediate medical attention. 1. Umbilical cord factor: If there are various conditions such as umbilical cord knot, umbilical cord around the neck, umbilical cord prolapse, etc., the flow of blood in the umbilical cord may be significantly affected, which may lead to lack of oxygen for the fetus, causing sudden disappearance of fetal heart sounds. 2. Fetal factors: If the fetus has congenital developmental abnormality or the embryo has poor growth and development, it may cause the embryo development to stop, causing the disappearance of fetal heart sound. 3. Maternal factors: If the pregnant woman has various pregnancy complications such as gestational hypertension syndrome, takes a large amount of drugs that cause fetal arrest, or long-term basic chemical substances or radioactive substances, it may cause fetal arrest and lead to the disappearance of fetal heart sound. If a pregnant woman has a sudden absence of fetal heartbeat, she needs to go to the obstetrics and gynecology department of the hospital in time for consultation and treatment.