Transvaginal sonography in the evaluation of normal early pregnancy: correlation with HCG level

Transvaginal sonography (TVS) is the procedure of choice in evaluating the viability of embryos early in pregnancy. However, viability based on TVS can be assessed more accurately when the exact gestational age from the last menstrual period is known or when the findings are correlated with beta human chorionic gonadotropin (HCG) levels. No large series has been reported with correlative data between early pregnancy findings, HCG, and gestational age. We performed 75 transvaginal examinations in 53 patients with proved normal pregnancy in the fifth through seventh weeks of gestation. The presence and size of the gestational sac, presence of a yolk sac, and identification of embryonic heart activity were correlated with the level of HCG. Sac size was correlated with yolk sac and heart activity and the three parameters correlated with gestational age in days. When the level of HCG reached 1000 mIU/ml by using the first International Reference Preparation, a gestational sac was seen sonographically in each patient. When the HCG level reached 7200 mIU/ml, a yolk sac was seen in every patient. Ten of 22 patients with HCG between 1000 and 7200 mIU/ml had a visible yolk sac. Every patient with an HCG level greater than 10,800 mIU/ml had a visible embryo with a heartbeat. A discriminatory level of 32 days was found for the presence of a gestational sac. A yolk sac was first seen in every patient between 36 and 40 days. Every patient with accurate dates greater than 40 days had an embryo with a heartbeat identified. When correlating sac size with structures within the sac, a yolk sac was first seen in a gestational sac between 6 and 9 mm and a heartbeat seen in every patient with a 9-mm or greater gestational sac diameter. These data allow identification of normal intrauterine pregnancy and distinction of normal from ectopic gestation at least 1 week earlier than is possible with transabdominal techniques.