when is fetal pole identified
With a transvaginal probe, a 3- to 4-mm gestational sac can usually be seen by 5 weeks from the last menstrual period (Fig. 1). A yolk sac or small fetal pole is usually seen by 6 menstrual weeks, when the mean diameter of the sac has reached 10 mm. As shown by Fossum and colleagues, the appearance of these structures can be correlated with Î²-human chorionic gonadotropin (Î²-hCG) levels (Table 2).