What transvaginal ultrasound findings are diagnostic of pregnancy failure in a 32-year-old woman (G3P0) at 7 weeks and 6 days pregnant by Last Menstrual Period (LMP)?

Transvaginal Ultrasound Findings Diagnostic of Pregnancy Failure

The correct answer is (d): Absence of embryo with heartbeat ≥11 days after a scan that showed a gestational sac with a yolk sac is definitively diagnostic of pregnancy failure. 1

Definitive Diagnostic Criteria for Pregnancy Failure

The following transvaginal ultrasound findings are definitively diagnostic of pregnancy failure and do not require follow-up imaging:

Crown-Rump Length Criteria

• CRL ≥7 mm without cardiac activity is diagnostic of embryonic demise 1, 2
• Option (a) with CRL of 5 mm and no heart rate does NOT meet diagnostic criteria and requires follow-up imaging in 7-10 days 1

Mean Sac Diameter Criteria

• MSD ≥25 mm without an embryo is diagnostic of pregnancy failure 1
• Option (b) with MSD of 20 mm does NOT meet diagnostic criteria—this is below the threshold and requires follow-up ultrasound 1

Time-Based Criteria with Yolk Sac

• Absence of embryo with cardiac activity ≥11 days after visualization of gestational sac WITH yolk sac is diagnostic of pregnancy failure 1
• This is option (d) and represents the correct answer

Time-Based Criteria without Yolk Sac

• Absence of embryo with cardiac activity ≥14 days after visualization of gestational sac WITHOUT yolk sac is diagnostic of pregnancy failure 1
• Option (c) states >10 days, which does NOT meet the required ≥14 day threshold 1

Why Each Answer is Correct or Incorrect

Option (a) - INCORRECT: A CRL of 5 mm without cardiac activity is concerning but not diagnostic. The definitive threshold is CRL ≥7 mm. 1, 2 At 5 mm, follow-up imaging should be performed rather than making a definitive diagnosis of pregnancy failure. 1

Option (b) - INCORRECT: An MSD of 20 mm without an embryo falls into the "concerning" category (16-24 mm range) but does not meet the ≥25 mm threshold required for definitive diagnosis. 1 This requires follow-up ultrasound in 7-10 days. 1

Option (c) - INCORRECT: The timeframe of >10 days is insufficient. The guideline requires ≥14 days after visualization of a gestational sac without a yolk sac to diagnose pregnancy failure definitively. 1

Option (d) - CORRECT: This meets the Society of Radiologists in Ultrasound consensus criteria requiring ≥11 days after visualization of a gestational sac with a yolk sac. 1 The presence of a yolk sac indicates more advanced development, hence the shorter required interval (11 days vs 14 days without yolk sac).

Critical Clinical Context

At 7 weeks 6 days gestation by LMP:

• Cardiac activity should be reliably visible by transvaginal ultrasound in a viable pregnancy 2
• Any measurable embryo should demonstrate cardiac activity 1, 2
• The discriminatory hCG level (approximately 3,000 mIU/mL) should be exceeded, making a gestational sac clearly visible 3

Essential Pitfalls to Avoid

• Never diagnose pregnancy failure on a single measurement without confirming absence of cardiac activity 1
• Ensure adequate time intervals between measurements before concluding abnormal growth 1
• Use transvaginal rather than transabdominal ultrasound for accurate first-trimester assessment 1
• Document exact measurements of CRL and MSD to avoid diagnostic errors 1
• Confirm gestational age by LMP to avoid dating errors that could lead to misdiagnosis 1