Fetal Pole (6 weeks)
A mass of fetal cells, separate from the yolk sac, first becomes apparent on transvaginal ultrasound just after the 6th
week of gestation. This mass of cells is known as the
fetal pole. It is the fetus in its somite stage. Usually you can identify rhythmic fetal cardiac movement within the fetal pole, although it may need to grow several mm before this is apparent.
The fetal pole grows at a rate of about 1 mm a day, starting at the 6th week of gestational age.