When does baby's heartbeat show up on ultrasound?

What does the evidence say about when you can see or hear baby's heartbeat on ultrasound during pregnancy?

1. A contemporary review of embryonic development explains that rhythmic cardiac activity begins early and that historical definitions of when the human embryonic heart starts beating differ from when ultrasound can visualize motion. 1
2. A first-trimester ultrasound review separates findings that are suspicious from findings diagnostic of early pregnancy loss: absence of cardiac activity with crown-rump length below 7 mm is suspicious, whereas a crown-rump length of at least 7 mm without activity is diagnostic under the listed criteria. 2
3. A first-trimester cardiac-function review reports that heart rate rises from the fifth through ninth gestational weeks and that transvaginal imaging offers earlier cardiac detail than transabdominal imaging in the first trimester. 3
4. The NCBI first-trimester ultrasound chapter states that a fetal pole may be visualized around six weeks and cardiac activity is usually evident by the sixth or seventh gestational week. 4
5. The NCBI early-pregnancy assessment chapter describes fetal cardiac activity and heart rate assessment by ultrasound and gives a broad six-to-eight-week range for fetal heart tones. 5

Is when you can see or hear baby's heartbeat on ultrasound safe in each trimester?

• First trimester. Early cardiac activity is commonly visible around 6 to 7 weeks, but a scan that is earlier than expected may show only a sac or yolk sac. Dating and repeat imaging matter.
• Second trimester. The early scan question is usually resolved by the second trimester. If an earlier report was uncertain, keep the follow-up appointment rather than interpreting one scan alone.
• Third trimester. This page concerns early ultrasound timing. Later pregnancy uses different imaging and monitoring methods, and a home Doppler cannot substitute for clinical assessment of symptoms or fetal well-being.