The absence of fetal heart on negative ultrasound has nothing to do with staying up late, the ultrasound only reflects the condition of the embryo at that time, but staying up late may lead to the absence of fetal heart. The absence of fetal heart may be related to embryonic factors, maternal factors and so on. 1. Embryonic factors: chromosomal abnormalities, including numerical and structural abnormalities, are common causes of embryonic abnormalities in early pregnancy. 2. Maternal factors: maternal systemic diseases or maternal uterine diseases, such as uterine septum and antiphospholipid syndrome, may lead to the absence of fetal heart. In addition, the short duration of pregnancy, the heart tube beat has not yet formed, or pregnant women smoking, staying up all night, etc. may occur ultrasound detection of fetal heart. Patients who do not have a detectable fetal heartbeat should consult their doctor and follow medical advice.