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. 

Transvaginal Ultrasound Accuracy

Transvaginal ultrasounds produce clear images of the fetus and uterus and surrounding structures that help doctors confirm the presence of a pregnancy, establish a pregnancy timeline, and gain insight into the health of the 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, problems such as 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. In addition, an ultrasound is helpful for: 

  • Confirming the location of a pregnancy and ensuring it is not an ectopic pregnancy (a pregnancy that has implanted outside the uterus in nearby structures, such as one of the fallopian tubes) 
  • Determining the number of fetuses you are carrying
  • Identifying an increased risk of miscarriage or pregnancy loss 
  • Checking the health of other pelvic organs

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. Thus, 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 visible (which is possible only if the measurements match a gestational age of 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.

Remember though that there are variations in when different types of ultrasounds are able to detect a heartbeat. A transvaginal ultrasound finds the heartbeat fairly early, usually between 6 and 7 weeks of gestation. An abdominal ultrasound will find the baby's heartbeat roughly one week later, or between 7 and 8 weeks of gestation. A handheld doppler ultrasound device (the kind OB/GYNs use during prenatal visits) may not be able to find a heartbeat until as late as 12 weeks.

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  2. 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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