The fetal heart begins to beat at approximately the same rate as the mother's, which is typically 80 to 85 bpm. 1  The approximate fetal heart rate for weeks 5 to 9 (assuming a starting rate of 80): 2  Week 5 starts at 80 and ends at 103 bpm. 3  Week 6 starts at 103 and ends at 126 bpm. 4  Week 7 starts at 126 and ends at 149 bpm.