Gestational Sac Discriminatory Levels of Serum HCG in Early Pregnancy Resulting in Live Birth

Abstract Our primary objective is to verify or refute a 2013 study by Connolly et al. which showed that in early pregnancy a gestational sac was visualized 99% of the time on transvaginal ultrasound when the HCG level reached 3,510 mIU/mL. Our secondary objective was to make clinical correlations by assessing the relationship between human chorionic gonadotropin (HCG) level in early pregnancy when a gestational sac is not seen with pregnancy outcomes of live birth, spontaneous abortion, and ectopic pregnancy. This retrospective study includes 144 pregnancies with an outcome of live birth, 87 pregnancies with an outcome of spontaneous abortion, and 59 ectopic pregnancies. Logistic regression is used to determine the probability of visualizing a gestational sac and/or yolk sac based on HCG level. A gestational sac is predicted to be visualized 50% of the time at an HCG level of 979 mIU/mL, 90% at 2,421 mIU/mL, and 99% of the time at 3,994 mIU/mL. A yolk sac was predicted to be visualized 50% of the time at an HCG level of 4,626 mIU/mL, 90% at 12,892 mIU/mL, and 99% at 39,454 mIU/mL. 90% of ectopic pregnancies presented with an HCG level below 3,994 mIU/mL. These results are in agreement with the study by Connolly et al. Since most early ectopic pregnancies had an HCG value below the discriminatory level for gestational sac visualization, other methods for evaluation of pregnancy of unknown location such as repeat HCG values are clinically important.