Does the fetal heart rate slow down when the fetus is sleeping?

Under normal circumstances, fetal heart rate may show physiological deceleration when the fetus is sleeping, which is considered normal. However, if the deceleration exceeds the normal range or is accompanied by other abnormalities, it is not considered normal and requires attention. The detailed analysis is as follows:

When the fetus is awake, it tends to be more active, and the fetal heart rate usually remains within the normal range of 140–160 beats per minute, and may even temporarily increase due to movement. When the fetus enters a sleep state, activity decreases and the body's metabolic rate slows down, leading to physiological slowing of the fetal heart rate, typically decreasing to 120–140 beats per minute. In some cases, it may briefly drop slightly below 120 beats per minute, but this usually does not last long and is not accompanied by abnormal fetal movements.

If the fetal heart rate continuously remains below 120 beats per minute, or shows significant deceleration accompanied by markedly reduced or absent fetal movement, it could be a sign of abnormal conditions such as intrauterine hypoxia or fetal distress, which are not normal and require prompt attention to the trend of fetal heart rate changes.

In daily life, pregnant women can use fetal movement counting as a preliminary method to assess fetal well-being. There is no need for excessive anxiety if fetal movements are normal. During the second and third trimesters, regular fetal heart rate monitoring under medical guidance is recommended. If transient fetal heart rate deceleration occurs during monitoring, the mother may try gentle physical activity or lightly tapping the abdomen to awaken the fetus before continuing observation.