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.
- 1. Winn HN, Hobbins JC. Clinical maternal-fetal medicine. Taylor & Francis. (2000) ISBN:1850707987. Read it at Google Books - Find it at Amazon
- 2. Merz E, Bahlmann F. Ultrasound in obstetrics and gynecology. Thieme Medical Publishers. (2005) ISBN:1588901475. Read it at Google Books - Find it at Amazon
- 3. Jain KA, Hamper UM, Sanders RC. Comparison of transvaginal and transabdominal sonography in the detection of early pregnancy and its complications. AJR Am J Roentgenol. 1988;151 (6): 1139-43. AJR Am J Roentgenol (abstract) - Pubmed citation
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