The development of the fetal heart happens surprisingly early in pregnancy. At only four weeks of gestational age, the fetal heart begins to beat. By six weeks, the heart typically beats between 100 and 120 times per minute.
By the second pregnancy ultrasound at RMA Lehigh Valley (at 6.5 weeks), we can actually watch the fetal heart beating on the screen and even measure the fetal heart rate. We don’t listen to the heart beating since the use of Doppler exposes the baby to higher frequency sound.
The ultrasound machine can calculate the heart rate when we measure the distance between the motion of the heart beats. From seven weeks gestational age and for the remainder of the pregnancy, the baby’s heart rate usually measures between 120 and 180 beats per minute. Compare that to a normal resting adult heart rate of 60 to 100 beats per minute and it’s quite a difference.