Are Ultrasounds Accurate for Finding a Baby's Heartbeat?

Types of ultrasounds and their uses

pregnant woman getting ultrasound
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There are two types of ultrasounds generally used to visualize a pregnancy: a transvaginal ultrasound, in which a probe is inserted into the vagina to gain proximity to the womb, and an abdominal ultrasound, which is placed on the mother's abdomen. Both are useful procedures for various circumstances and have their place in prenatal care. 

Abdominal ultrasounds are generally very effective after 8 weeks gestation. Therefore, if you are having an ultrasound prior to 8 weeks from your last menstrual period, it will most likely be a transvaginal ultrasound. 

When Is a Transvaginal Ultrasound Performed?

Transvaginal ultrasounds produce clear images of the fetus, uterus, and surrounding structures, all of which help doctors confirm pregnancy, establish a pregnancy timeline, and gain insight into the health of the pregnancy.

In addition, an ultrasound is helpful for: 

  • Checking the health of your pelvic organs
  • Determining the number of fetuses you are carrying
  • Identifying your risk of miscarriage
  • Pinpointing the location of the pregnancy (normal or ectopic pregnancy)

While not all women will have an early pregnancy ultrasound, some are more likely to be referred for one than others. For example, if you have experienced vaginal bleeding, a miscarriage in a previous pregnancy, or other circumstances that make you or your healthcare provider more alert to potential problems, you may be referred for an early pregnancy ultrasound.

Accuracy in Confirming the Heartbeat

A transvaginal ultrasound can detect a heartbeat with very high accuracy as early as six or seven weeks into a pregnancy. If performed properly, the results are considered accurate and reliable.

Remember though that there are variations in when different types of ultrasounds are able to detect a heartbeat.

  • Transvaginal ultrasounds find the heartbeat fairly early, usually between 6 and 7 weeks of gestation.
  • Abdominal ultrasounds find the baby's heartbeat roughly one week later, or between 7 and 8 weeks of gestation.
  • Handheld Doppler ultrasound devices (the kind OB/GYNs use during prenatal visits) may not be able to find a heartbeat until as late as 12 weeks.

Why a Fetal Heartbeat May Not Be Detected

A transvaginal or abdominal ultrasound showing no fetal heartbeat will mean one of two things: either the pregnancy is too early along for the heartbeat to be detected (which is possible if gestational age is 7 weeks or earlier), or a pregnancy loss has occurred. Note that this does not necessarily apply to handheld doppler devices, which do not detect the heartbeat until later.

Any time an ultrasound fails to find a fetal heartbeat after one has previously been seen, the doctor can conclusively diagnose miscarriage. In addition, when there is no heartbeat in a pregnancy that is definitely far enough along that the heartbeat should be visible, the ultrasound results definitely mean miscarriage.

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  3. Condous G. Ultrasound diagnosis of miscarriage: new guidelines to prevent harm. Australas J Ultrasound Med. 2011;14(4):2. doi:10.1002/j.2205-0140.2011.tb00127.x

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