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The presence of heart activity, as seen here, indicates a live fetus at the time of the ultrasound exam. If a pregnancy is going to fail, it will normally fail early, usually before 7 weeks. Therefore, the predictive value of fetal heartbeat depends on the menstrual age at the time of the exam. After 7 weeks, pregnancy loss rate is 2-2.3%. After 16 weeks, the loss rate is 1%. In embryos less than 6.5 weeks menstrual age, demonstration of heart activity is associated with a failure rate of 24%.
Note, however, that absence of a heartbeat is not necessarily abnormal. With endovaginal sonography (EVS), normal embryos less than 4 to 5 mm may show no cardiac activity. The absence of cardiac activity in larger embryos is diagnostic of fetal demise.
Forward to Case 20: Ectopic Pregnancy
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