Fetal pole

Last revised by Dr Jeremy Jones on 20 Sep 2021

The fetal pole is the first direct imaging manifestation of the fetus and is seen as a thickening on the margin of the yolk sac during early pregnancy. It is often used synonymously with the term "embryo".

The fetal pole is usually identified at ~6.5 weeks with transabdominal ultrasound imaging and at ~6 weeks 2 with transvaginal ultrasound imaging, although it may not be seen until ~9 weeks in some cases.

  • a fetal pole should be seen when MSD ≥16 mm on TVS (by RCOG criteria), or MSD ≥25 mm on TAS
  • pregnancy failure is not diagnosed until a fetal pole is not seen when MSD ≥25 mm on TVS

When the fetal pole measures ≥7 mm, a fetal heartbeat should be detected.

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Cases and figures

  • Case 1: showing fetal pole adjacent to yolk sac
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