Normal Fetal Heart Rate Ranges in Early Pregnancy

Female technologist performing ultrasound on patient
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The normal fetal heart rate usually varies somewhere between 120 and 160 beats per minute (bpm) throughout pregnancy, but in the early part of the first trimester, the baby's heart rate can be slower. A 1996 study established the following as the minimum normal heart rates in early pregnancy ultrasounds, with the size varying by the size of the fetal pole:

  • 2 mm embryo: 75 beats per minute
  • 5 mm embryo: 100 beats per minute
  • 10 mm embryo: 120 beats per minute
  • 15 mm embryo: 130 beats per minute

Slow or Fast Heartbeats

Although viable pregnancies can occasionally have initial heart rates lower than these norms, a slow heart rate in early pregnancy is associated with a higher risk of miscarriage. Doctors usually recommend followup ultrasounds for women whose babies have slow heart rates in order to determine whether or not the pregnancy is viable. Unfortunately, nothing can be done to affect the outcome; a miscarriage that happens after detecting a slow heart rate sometimes means the baby had chromosomal abnormalities from the beginning.

A faster than normal heart rate does not appear to carry an increased risk of miscarriage or other negative pregnancy outcomes.

There is no evidence that the fetal heart rate can predict the baby's gender.

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Article Sources

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  1. Doubilet PM, Benson CB. Embryonic heart rate in the early first trimester: what rate is normal?. J Ultrasound Med. 1995;14(6):431-4. doi:10.7863/jum.1995.14.6.431

  2. Coulam CB, Britten S, Soenksen DM. Early (34-56 days from last menstrual period) ultrasonographic measurements in normal pregnancies. Hum Reprod. 1996;11(8):1771-4. doi:10.1093/oxfordjournals.humrep.a019483

  3. Stefos TI, Lolis DE, Sotiriadis AJ, Ziakas GV. Embryonic heart rate in early pregnancy. J Clin Ultrasound. 1998;26(1):33-6.

  4. Doubilet PM, Benson CB, Chow JS. Outcome of pregnancies with rapid embryonic heart rates in the early first trimester. AJR Am J Roentgenol. 2000;175(1):67-9. doi:10.2214/ajr.175.1.1750067

Additional Reading

  • Cardiovascular System Development - Embryonic Heart Rate. Mark Hill. UNSW Embryology.