Answer: Use M-mode instead of pulse-wave Doppler to measure the fetal heart rate.
Explanation: M-mode is a famous ultrasound process during the early days of Ultrasound technologies, M-mode has a very high sampling rate. One of the major disadvantages is that it may be difficult to align the M-mode to be the perpendicular to the SEPTUM. M-mode has only one (1) dimensional view of an object,to minimize the risk to the Fetus, M-mode is the most applicable tradeoff. Specifically, M-mode is mainly used because of its Axial and temporal resolution of the structure of objects.