Starting at around 20 weeks, the fetal heartbeat can usually be heard without Doppler amplification (ultrasound). At this point a special stethoscope called a fetoscope can be used. The heartbeat is best heard over the baby's back, which often seems firm when you feel around the uterus. It may be difficult to hear the fetal heart by stethoscope if the mother is overweight or if the placenta is on the front wall of the uterus.