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How early can I hear the fetal heartbeat?
Q: I’m pregnant for the third time. I have a 5-year-old and my last pregnancy was a miscarriage. I wonder how often the heartbeat is heard at 10 weeks in the doctor’s office. I was not able to hear the heartbeat at 10 weeks with my miscarriage and am worried that I will miscarry again if I don’t hear it this time. I’m a petite woman and I’m not overweight.
A: After a miscarriage, it is understandable that you would feel anxious to hear the fetal heartbeat as early as possible. The fetal heart rate monitor, or Doppler, will sometimes be able to detect a heartbeat as early as eight to 10 weeks. It does this by sending out small, high frequency sound waves and detecting their reflection off the pulsing fetal heart. These reflected signals are processed and amplified to enable you to hear the fetal heart.

The fetal heart beats more rapidly than your own heart rate, usually between 120 and 160 beats per minute. Whether you’ll be able to hear the heartbeat is a combination of your own anatomy and luck. The embryo at 10 weeks is very small, slightly bigger than an inch. If you are thin, and your uterus is positioned “anteriorly,” close to your abdominal wall, it makes it easier for your doctor to detect a fetal heartbeat. If your uterus is positioned “posteriorly,” that is, closer to your back, it will be harder to find the heartbeat.

Also, keep in mind that the Doppler transmits sound waves along a particular pathway. A slight change in the angle of the machine can cause the sound waves to miss the embryo. It’s a little like looking for a needle in a haystack.

If your doctor is unable to detect a fetal heartbeat at 10 weeks you can request an ultrasound of the pregnancy. The ultrasound, also called a sonogram, uses sound waves to provide a visual picture of your uterus and the pregnancy. The ultrasound can be used abdominally or intravaginally, allowing detection of an embryo and fetal heart movements as early as seven weeks gestation. The intravaginal ultrasound usually provides a good picture regardless of the position of your uterus. Although the ultrasound image doesn’t provide an audible heartbeat, the visual flutter of the heart can be extremely reassuring, and will let you and your doctor know whether your pregnancy is off to a good start.

Laura E. Stachel M.D. Obstetrician & Gynecologist