Using transvaginal USG, the gestational sac can usually be seen at 4 weeks, the yolk sac at 5 weeks, and the fetal pole with cardiac activity by 6 weeks. Cardiac activity can be seen simultaneously with the appearance of a fetal pole as a pulsation at the lateral aspect of the yolk sac. Normal embryonic hea rate may be as low as 70-100 beats per minute range during early gestation, but soon rises to the fetal normal range of 120-160 beats/min by 9-10 weeks gestational age.