Sinus tachycardia in pregnant women is mostly caused by a sudden increase in activity, iron deficiency anemia, thyroid dysfunction, or an increased burden on the heart in late pregnancy. 1. Sudden increase in activity: for example, recent fatigue or walking too fast may cause a sudden increase in the demand for blood supply, the body’s blood supply can not meet the demand will appear tachycardia. This kind of tachycardia can be relieved by itself after rest. 2. Iron deficiency anemia: because pregnant women themselves have anemia symptoms, the body’s blood supply is insufficient, then it will also cause tachycardia, need to take oral iron supplements, and usually increase the nutritional improvement. 3. Thyroid dysfunction: it is due to the thyroid hormone affects the function of the heart sinus node cells, if the thyroid dysfunction, it will be combined with the pregnant woman to appear the symptoms of panic, accelerated heart rate, the need for timely examination, according to the extent of the condition of the treatment. 4. Increased heart burden in late pregnancy: due to the change of blood circulation during pregnancy, the heart burden will be increased because of the burden of pregnant women and fetus blood circulation, until the blood supply is insufficient, it will be easy to panic, rapid heart rate symptoms. Clinically, if pregnant women have symptoms of tachycardia, they need to consult a doctor in time, under the guidance of the doctor to clarify the specific causes of the disease, and give targeted treatment to avoid delaying the condition.