The fourth month of pregnancy is the 16th week of pregnancy, at which time the fetus is completely located in the abdominal cavity, and the fetal heartbeat can usually be heard near the midline below the navel of the pregnant woman. However, because the fetus is still small, the use of an ordinary stethoscope is generally inaccurate, usually need to use a Doppler stethoscope. If you can not hear the fetal heart, the main reasons include the following: 1, abnormal fetal position: if the fetal position is not good or the heartbeat is located in the back, near the spine of the pregnant woman, resulting in unclear hearing, can be in the pregnant woman appropriate activities and then re-listening to the fetal heart; 2, thick abdominal wall: if the pregnant woman’s abdominal wall is thin, in the 4th trimester of pregnancy with a stethoscope can be heard the fetal heart, but if the pregnant woman is thicker abdominal wall, and sometimes the 5th trimester of pregnancy To use the stethoscope to hear the fetal heart, and may even require a larger gestational weeks; 3, weak fetal heart: if the fetal heart is weak, there is a possibility of inaudible or inaudible, this time you need to keep the room quiet, quietly and carefully listening to the diagnosis, if still can not be heard, the use of ultrasound detection; 4, no fetal heart: that is, the embryo is inactivated, at this time the use of the stethoscope can not be heard the heart of the fetus, you need to review the ultrasound to determine the diagnosis, after the diagnosis is clear and timely termination of pregnancy as prescribed by the doctor. After the diagnosis is clear, follow the doctor’s advice to terminate the pregnancy in a timely manner. Normal fetal heart rate in the fourth month of pregnancy is 110-160 beats/min, if the fetal heart rate lasts more than 10 minutes <110 beats/min or >160 beats/min, it indicates that the fetal heart rate is abnormal, there may be intrauterine hypoxia of the fetus, or by the pregnant woman’s own condition affects the fetal heart rate changes, such as fever, taking medication, or hyperthyroidism and so on.