Whether 166 bpm is normal or not depends on the situation. Under normal circumstances, the fetal heart rate is 110-160 beats/min in early pregnancy and 120-160 beats/min in mid and late pregnancy. In early pregnancy, the fetal primitive heart tube is immature and the pregnant woman is emotionally stressed, the heart rate will increase and the fetal heart rate will also increase. The fetal heart rate can be 166 beats/min, but it is only transient and will fall back to the normal level in a short time, which is normal and no special treatment is needed, just follow up and observe. If the fetal heart rate is often too fast and stays above 160 beats/min, especially in the middle and late pregnancy, it is most likely due to intrauterine hypoxia, which is a sign of abnormality. Pregnant women can administer oxygen and change position to improve maternal blood oxygen level, thus increasing the oxygen level in the placenta and relieving intrauterine hypoxia of the fetus, while closely monitoring the fetal heart changes. If there is no improvement after oxygenation, a cesarean section is needed to end the delivery when the conditions of the pregnant woman and the fetus allow. In case of abnormal fetal heartbeat, the pregnant woman should first pay attention to relaxing her mind and seek medical examination in time. If there is no abnormality, she can go home and continue to recuperate, but she should eat lightly, avoid strenuous exercise, keep an eye on the fetus and monitor the fetal heartbeat.