Absence of Fetal Cardiac Activity at 8 Weeks Gestation
At 8 weeks gestation, the absence of fetal cardiac activity is diagnostic of embryonic demise and will inevitably result in spontaneous abortion—the pregnancy cannot continue. 1, 2
Definitive Diagnostic Criteria
The diagnosis is confirmed when transvaginal ultrasound demonstrates:
- Crown-rump length (CRL) ≥7 mm without cardiac activity confirms embryonic demise with 100% certainty 1, 2
- At 8 weeks gestation, the expected CRL is approximately 14-20 mm, well above the 7 mm diagnostic threshold 2
- Mean sac diameter (MSD) ≥25 mm without a visible embryo also confirms pregnancy loss 1, 2
These criteria from the Society of Radiologists in Ultrasound 2024 consensus guidelines are designed to avoid false-positive diagnoses while providing definitive confirmation of embryonic demise. 1, 2
Clinical Implications and Natural History
Once embryonic demise is confirmed at 8 weeks:
- The pregnancy will not progress—spontaneous expulsion of tissue will occur, though timing varies 3, 4
- Expectant management (waiting for spontaneous passage) is contraindicated due to increased risks of intrauterine infection, coagulopathy, and maternal sepsis with prolonged retention 3
- The appropriate terminology is "embryonic demise" or "missed abortion" rather than outdated terms like "blighted ovum" 1, 3, 2
Risk Context: When Cardiac Activity IS Present
To understand the significance of absent cardiac activity, consider that when fetal cardiac activity is documented at 8 weeks in asymptomatic women, the subsequent miscarriage risk drops to only 1.5% 5. The presence of cardiac activity at this gestational age is highly predictive of ongoing pregnancy viability. 5, 6
Conversely, absence of cardiac activity at 8 weeks with a measurable embryo definitively indicates pregnancy loss. 1, 2
Management Recommendations
Active evacuation via medical or surgical methods should be offered immediately rather than expectant management: 3
- Surgical evacuation (vacuum aspiration) has the lowest complication rates: hemorrhage 9.1%, infection 1.3%, retained tissue 1.3% 3
- Medical management with mifepristone 200 mg + misoprostol 800 mcg achieves approximately 80% success rate for missed abortion 3, 4
- Expectant management carries significantly higher maternal morbidity (60.2% vs 33.0% with active treatment), intraamniotic infection (38.0% vs 13.0%), and postpartum hemorrhage (23.1% vs 11.0%) 3
Critical Preventive Measure
All Rh-negative women must receive 50 μg anti-D immunoglobulin to prevent alloimmunization, as fetomaternal hemorrhage occurs in 32% of spontaneous abortions. 3, 2
Common Pitfall to Avoid
Never diagnose embryonic demise if the CRL is <7 mm, even if cardiac activity is absent—a follow-up scan in 7-10 days is required in that scenario to avoid misdiagnosis due to dating errors. 1, 2 However, at 8 weeks gestation with expected CRL of 14-20 mm, this concern does not apply if proper measurements are obtained. 2