From the Guidelines
The fetal pole, now more accurately referred to as the embryonic pole, is typically visible on an ultrasound at approximately 6 weeks gestational age (GA), as indicated by the Society of Radiologists in Ultrasound consensus conference recommendations 1.
Key Points to Consider
- The visibility of the embryonic pole on ultrasound is a significant milestone in early pregnancy development, marking the point at which the embryo itself becomes visible, distinct from the gestational sac and yolk sac.
- According to the most recent guidelines, the term "fetal pole" is considered obsolete, and "embryonic pole" or simply measuring the crown-rump length (CRL) is preferred for describing the embryo before 11 weeks GA 1.
- The embryonic pole is usually seen on transvaginal ultrasound (TVUS) at about 6 weeks GA, with cardiac activity becoming detectable around the same time or shortly after, typically reported as cardiac activity or cardiac motion rather than "heartbeat" to avoid implying a fully formed organ 1.
- It's crucial to understand that the timing of when the embryonic pole becomes visible can vary slightly due to factors like the accuracy of pregnancy dating and individual developmental variations.
- If the embryonic pole is not visible by 7 weeks on a TVUS when the dates are certain, it may indicate a non-viable pregnancy, but follow-up ultrasound is recommended for confirmation, as the absence of visible embryonic development at this stage does not definitively diagnose a non-viable pregnancy without considering other clinical factors 1.
From the Research
Fetal Pole Detection on Ultrasound Pregnancy
- The detection of a fetal pole on ultrasound pregnancy is a significant milestone in pregnancy monitoring.
- According to a study published in 1988 2, a fetal pole can be seen approximately 40.3 +/- 3.4 days from the last menstrual period (LMP) when the hCG level is around 5113 +/- 298 mIU/ml of the IRP or 3783 +/- 683 mIU/ml of the second IS.
- This study used transvaginal ultrasonography to detect an intrauterine gestation earlier than what has been previously reported with transabdominal ultrasonography.
- Other studies have focused on the diagnosis of non-viable gestational sacs and the prediction of viability in intrauterine pregnancies of uncertain viability (IPUVs) 3, 4, 5.
- However, these studies do not provide specific information on when a fetal pole can be detected on ultrasound pregnancy.
- A more recent article published in 2023 6 reviews the use of ultrasound in pregnancy, including techniques for transabdominal and transvaginal studies, but does not provide specific information on fetal pole detection.
- In summary, the detection of a fetal pole on ultrasound pregnancy can be expected around 40.3 +/- 3.4 days from the LMP, as reported in the 1988 study 2.