There is no specific time and it may be related to the amount of amniotic fluid, whether the placenta is ruptured, etc. The fetus survives in the amniotic fluid in the mother’s uterine cavity. The amniotic fluid will have a cushioning effect on external pressure and can protect the baby from external pressure, but if external pressure persists on the uterus or if the amniotic fluid volume in the uterine cavity is too low, the cushioning effect of the amniotic fluid is weakened or disappears and the baby will be subjected to external pressure. With the aid of prenatal fetal heart monitoring, if the fetal heart rate is abnormal, manifesting as ≥160 beats per minute or <100 beats per minute, it may be associated with asphyxia.