Definition:
Fetal pole, a thick spot near the yolk sac, is the term used for the earliest signs of a baby in an early pregnancy ultrasound -- before the baby has formed a recognizable human shape. With a transvaginal ultrasound, the fetal pole becomes visible around 6 weeks of gestation.
If you are curious about the origin of the term, it comes from the use of "pole" to describe one of two morphologically different areas at the ends of an axis in an organism. In a newly developing baby, the fetal pole appears as a thick area on the side of the yolk sac, so it is a "pole" that is different from the rest of the yolk sac and which will ultimately become a fetus (baby).
