At what gestational age is a fetal pole typically visible during an ultrasound examination?

When is a Fetal Pole Seen on Ultrasound?

Direct Answer

The embryo (not "fetal pole") is typically visible on transvaginal ultrasound at approximately 6 weeks gestational age. 1, 2

Important Terminology Update

The term "fetal pole" is obsolete and should be avoided in modern practice. 3 The correct terminology is:

• "Embryo" for conceptus ≤10 weeks 6 days gestational age 3, 1
• "Fetus" beginning at 11 weeks 0 days gestational age 3, 1

Sequential Timeline of Early Pregnancy Visualization

The structures appear in this order on transvaginal ultrasound:

5 Weeks Gestational Age

• Gestational sac is the earliest finding, appearing as a round or oval fluid collection with a hyperechoic rim 3, 1, 2
• Gestational sacs as small as 2-3 mm in mean sac diameter may be visible 2

5½ Weeks Gestational Age

• Yolk sac becomes visible as a thin-rimmed circular structure 3, 1
• The presence of a yolk sac provides incontrovertible evidence of pregnancy 1, 2

6 Weeks Gestational Age

• Embryo with cardiac activity is typically visualized 1, 2
• Research confirms the embryo and cardiac activity can be detected as early as 34 days from last menstrual period with transvaginal ultrasound 4
• Cardiac activity is detectable in embryos with crown-rump length ≥3 mm 4

7 Weeks Gestational Age

• Amnion becomes visible 1, 2

Clinical Measurement Guidelines

Once an embryo is measurable, crown-rump length (CRL) should be used for dating, as it is more accurate than mean sac diameter. 3, 1

Critical Pitfalls to Avoid

Timing Considerations

• No ultrasound can visualize pregnancy at 2 weeks gestational age because conception has not yet occurred (ovulation occurs at 2 weeks GA) 2
• The earliest clinically useful transvaginal ultrasound should be performed at approximately 5 weeks gestational age or later 2

Diagnostic Criteria for Pregnancy Failure

• Absence of embryo in gestational sac >16 mm indicates poor prognosis 1
• Absence of cardiac activity in embryo ≥7 mm CRL is definitive for embryonic demise 1, 2
• For embryos <7 mm CRL without cardiac activity, follow-up ultrasound in 7-10 days is recommended 1, 2
• An "empty amnion" (visible amnion without embryo) is always associated with pregnancy loss 5

Reporting Standards

• Before visualizing yolk sac or embryo, report as "probable gestational sac" or "probable pregnancy" 3, 1
• With yolk sac present, report as "definite gestational sac" or "definite pregnancy" 3, 1
• Report cardiac activity as "cardiac activity" or "cardiac motion", avoiding terms like "heartbeat" or "heart motion" 1, 2

Correlation with hCG Levels

A gestational sac should be visible when hCG reaches approximately 1000-2000 mIU/mL, though levels up to 3000 mIU/mL may be needed to reliably exclude normal intrauterine pregnancy. 2