From the Guidelines
A fetal heartbeat can typically be detected at 6 weeks gestational age using transvaginal ultrasound, as rhythmic pulsations in the embryo/fetus become visible at this stage 1.
Detection of Fetal Heartbeat
The detection of cardiac activity is a significant milestone in fetal development, and it is essential to use accurate terminology when describing this phenomenon. According to the Society of Radiologists in Ultrasound consensus conference recommendations, cardiac activity should be reported as "cardiac activity" or "cardiac motion" instead of using terms like "heartbeat" or "heart motion" 1.
Gestational Age and Detection
The gestational age at which a fetal heartbeat can be detected is crucial in determining the viability of the pregnancy. At 6 weeks gestational age, the embryonic pole is visible on transvaginal ultrasound, and cardiac activity can be detected using M-mode or cine clip 1. It is essential to note that the detection of cardiac activity at this stage does not necessarily imply a fully formed heart, but rather the presence of rhythmic pulsations in the embryo/fetus.
Importance of Accurate Terminology
The use of accurate terminology is vital in obstetric ultrasound to avoid confusion and misinterpretation of findings. The Society of Radiologists in Ultrasound recommends avoiding terms like "heart" and "viable" in the first trimester, as they may imply a level of development that is not yet present 1. Instead, terms like "cardiac activity" and "embryo/fetus" should be used to describe the findings.
Clinical Implications
The detection of cardiac activity at 6 weeks gestational age has significant clinical implications. It can help confirm the presence of a viable pregnancy and provide reassurance to patients. However, if cardiac activity is not detected at this stage, it is essential to repeat the ultrasound 1-2 weeks later to confirm the findings, as the absence of cardiac activity does not necessarily indicate a non-viable pregnancy 1.
From the Research
Detection of Fetal Heartbeat
- The detection of a fetal heartbeat can be achieved through transvaginal Doppler auscultation as early as 6 weeks of gestation 2.
- Transvaginal ultrasonography is the preferred method for detecting fetal heart rate prior to 12 weeks of gestation, with a detection rate of 60.5% at 8 weeks and 87.5% at 9 weeks 2.
- Transabdominal Doppler auscultation can also detect fetal heart rate, but with lower sensitivity than transvaginal auscultation, with detection rates of 22.9% at 8 weeks and 56% at 9 weeks 2.
- The earliest fetal heart rate detected transvaginally was at 6 weeks 0 days of gestation, while the earliest detection transabdominally was at 7 weeks 0 days 2.
Gestational Age and Detection Methods
- Transvaginal ultrasound is the preferred route for fetal cardiac examination prior to 12 weeks of gestation, while transabdominal ultrasound can be used after 12 weeks 3.
- The 4-chamber view and outflow tracts are the most important planes for identification of an abnormal heart, and can be obtained in the majority of fetuses from 11 weeks of gestation onward 3.
- Additional ultrasound techniques, such as spatiotemporal image correlation and the evaluation of volumes by a fetal-heart expert, can improve the detection of congenital heart disease 3.
Prognostic Value of Fetal Heart Motion
- The presence of fetal heart motion seen during an early accurately dated transvaginal ultrasound is associated with a low risk of spontaneous abortion in women under 36 years of age 4.
- However, the presence of heart motion should not be considered a reassuring sign in older women, as the incidence of spontaneous abortion increases with age 4.
- The detection of fetal cardiac abnormalities can be achieved through transvaginal sonography at 12-16 weeks' gestation 5.
Early Detection of Pregnancy
- Transvaginal ultrasonography can detect an intrauterine gestation earlier than transabdominal ultrasonography, with a gestational sac visible at 34.8 +/- 2.2 days from the last menstrual period 6.
- Fetal heart motion can be detected by transvaginal ultrasonography at 46.9 +/- 6.0 days from the last menstrual period 6.