I. Introduction
In recent years, the number of pregnant women in China has remained above 13 million over the past decade[1] In addition, with the improvement of economic level and health awareness, people pay more attention to the health of pregnant women. Therefore, the health monitoring of the fetus is particularly important. Fetal heart rate (FHR) is critical in fetal heart monitoring[2]. The traditional fetal heart rate monitoring mainly relies on pregnant women to go to the hospital for regular check-up. However, going to the hospital frequently will greatly increase the physical burden of pregnant women and the pressure of hospital resources, so the development of at-home Doppler fetal heart monitor can effectively provide convenience for pregnant women who can achieve fetal monitoring at home.