The fetal heart rate is measured during every obstetric ultrasound examination and is one of the earliest signs of a viable pregnancy. Normal fetal heart rate varies by gestational age but is generally between 110 and 160 beats per minute during the second and third trimesters. On early ultrasound, fetal cardiac activity can first be detected at about 6 weeks of gestational age using transvaginal ultrasound. Abnormalities in fetal heart rate, including bradycardia below 110 and tachycardia above 160 beats per minute, can indicate fetal distress, arrhythmias, or other complications requiring further evaluation. M-mode ultrasound is the recommended method for documenting fetal heart rate because it does not expose the fetal heart to Doppler energy.
Sonography Term