What is "Embryonic Pole" on Ultrasound?
The term "embryonic pole" is obsolete terminology that should no longer be used in ultrasound reporting—the correct term is simply "embryo." 1
Understanding the Outdated Terminology
The word "pole" (as in "embryonic pole" or "fetal pole") was historically used to describe the early developing embryo visualized on ultrasound, but current consensus guidelines from the Society of Radiologists in Ultrasound explicitly state this terminology is obsolete and should be avoided. 1
What the Term Historically Referred To
When clinicians previously used "embryonic pole," they were referring to:
- The embryo itself visualized within the gestational sac on transvaginal ultrasound, typically first seen at approximately 6 weeks gestational age 2, 3
- A structure that appears as a thickening along the margin of the yolk sac before developing into a clearly defined embryonic form 4
- The earliest visible form of the developing conceptus before distinct anatomical features become apparent 5
Current Correct Terminology
Simply use "embryo" instead of "embryonic pole." 1
Key Definitions:
- Embryo: The correct term for the conceptus from when it becomes visible (approximately 6 weeks gestational age) through 10 weeks 6 days gestational age 1, 2
- Fetus: Beginning at 11 weeks 0 days gestational age, the conceptus should be referred to as a fetus 1, 2
Measurement Standards
Crown-rump length (CRL) is the proper measurement term for an embryo or fetus, representing its greatest dimension. 1, 2
- As soon as an embryo is measurable, CRL should be used for dating since it is more accurate than mean sac diameter 1, 2
- CRL measurements provide the most accurate gestational age assessment in the first trimester 6
Clinical Context for Visualization
Understanding the timeline helps clarify what structures should be visible:
- 5 weeks GA: Gestational sac visible (round/oval fluid collection with hyperechoic rim) 1, 2, 3
- 5½ weeks GA: Yolk sac visible (definitive evidence of pregnancy) 1, 2, 3
- 6 weeks GA: Embryo with cardiac activity typically visible 1, 2, 3
- 7 weeks GA: Amnion visible 2, 3
Important Clinical Pitfalls
Avoid using "embryonic pole" in reports as it perpetuates outdated terminology that has been formally replaced by consensus guidelines. 1
When an amnion is visible but no embryo is identified (the "empty amnion" sign), this indicates early pregnancy failure, particularly when the gestational sac measures >16 mm. 7
The absence of a visible embryo when expected based on gestational age or sac size requires careful correlation with clinical parameters and often follow-up imaging to confirm viability or pregnancy loss. 4, 7