First trimester fetal cardiac activity. Sonographic documentation of a progressive early rise in heart rate.
The heart rates of 124 first trimester fetuses were determined with real-time sonography and were analyzed with regard to gestational age. The mean embryonic heart rate increased from 101 beats per minute (bpm) at 5 to 5.95 menstrual weeks to 143 bpm at 8 to 8.95 weeks. After nine weeks, the rate reached a plateau, ranging from 137 to 144 bpm. Slower heart rates are normal early in the first trimester and should not be misinterpreted as an abnormal finding or mistaken for maternal pulsations.
Hertzberg, BS; Mahony, BS; Bowie, JD
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