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Significance of Cardiac Activity on Endovaginal Ultrasound in Very Early Embryos

Objective To evaluate the significance of cardiac activity on endovaginal ultrasound in embryos up to 10 mm in size. Methods Ninety–six women with positive urinary pregnancy tests had vaginal probe ultrasound examinations at the first clinical visit. All had discernible embryos between 1– mm in greatest length. The presence or absence of discernible cardiac activity was recorded. None of the subjects had any antecedent bleeding. All were available for follow–up until delivery or completion of a failed pregnancy. Results Seventy–four women had cardiac activity present at the initial study and 22 did not. Eighty-one delivered healthy newborns and 15 had early pregnancy failure. All embryos that ultimately proved normal showed cardiac activity by the time they were 4 mm in size. However, absence of detectable cardiac activity in embryos of 3 mm or less was still associated with a 41% continuation rate. Conclusions Cardiac activity is present in normal embryos before it can be detected on ultrasound. There are variations in the type and frequency of ultrasound equipment, maternal anatomical characteristics (obesity, coexisting fibroids, uterine version), and in the visual acuity of observers. Nevertheless, we conclude that in our hands, the absence of cardiac activity in embryos measuring 4 mm or more is reliably associated with embryonic death. In contrast, the lack of cardiac activity in embryos of 3 mm or less is nondiagnostic and may warrant follow–up study in 3–days.