Fetal Heart Observation How many weeks into pregnancy can the fetal heart rate be observed? Generally speaking, fetal heartbeat can be observed through B-ultrasound starting from the 6th week. As the fetus develops, the fetal heart rate also changes. The fetal heart rate is 100-130 beats/min from the 6th to 10th week, 130-160 beats/min from the 11th to 14th week, and then gradually drops to 120-140 beats/min. Observing the fetal heart rate is very important to determine whether the fetus is healthy. If the fetal heart rate is too fast