Diagnostic Criteria for Missed Abortion
A missed abortion (now termed "embryonic/fetal demise" or "anembryonic pregnancy") is definitively diagnosed on transvaginal ultrasound when: (1) crown-rump length (CRL) ≥7 mm with no cardiac activity, OR (2) mean sac diameter (MSD) ≥25 mm with no embryo, OR (3) absence of embryo with cardiac activity ≥14 days after visualization of gestational sac without yolk sac. 1
Definitive Diagnostic Criteria (Transvaginal Ultrasound)
The 2025 Society of Radiologists in Ultrasound consensus establishes these diagnostic thresholds 1:
For Embryonic/Fetal Demise:
- CRL ≥7 mm with no cardiac motion
- When gestational age ≥11 weeks 0 days, use term "fetal demise"
For Anembryonic Pregnancy:
- MSD ≥25 mm with no embryo visible
- ≥14 days after initial scan showing gestational sac without yolk sac, and still no embryo with cardiac activity present
These criteria are intentionally conservative to avoid false-positive diagnoses and inappropriate intervention in viable pregnancies.
"Concerning for" Early Pregnancy Loss (Not Yet Diagnostic)
The guidelines distinguish between definitive and concerning findings. These findings raise suspicion but require follow-up imaging 1:
- CRL <7 mm with no cardiac activity
- MSD 16-24 mm with no embryo
- Absence of embryo with cardiac activity 7-13 days after visualized gestational sac without yolk sac
Critical pitfall: Do not diagnose missed abortion based on these "concerning" criteria alone—repeat ultrasound in 7-14 days is mandatory to avoid misdiagnosing a viable pregnancy.
Clinical Context
Terminology Evolution
The term "missed abortion" is outdated 2. Current preferred terminology includes:
- Embryonic/fetal demise (when embryo/fetus visible)
- Anembryonic pregnancy (when no embryo develops; replaces "blighted ovum")
- Early pregnancy loss (EPL) as umbrella term
Clinical Presentation
While 92% of patients present with vaginal spotting 3, clinical symptoms alone are unreliable for diagnosis (kappa = 0.33 for history alone, 0.57 after physical exam) 4. Transvaginal ultrasound achieves diagnostic accuracy of kappa = 0.96 4.
Additional Ultrasound Findings
Poor prognostic indicators that support (but don't independently diagnose) EPL 1:
- Calcified yolk sac
- Expanded amnion sign (enlarged amniotic cavity relative to CRL)
- Gestational sac in lower uterine segment or endocervical canal
Algorithmic Approach
- Perform transvaginal ultrasound (transabdominal insufficient for early pregnancy)
- Measure CRL if embryo visible: ≥7 mm without cardiac activity = diagnostic
- Measure MSD if no embryo visible: ≥25 mm = diagnostic of anembryonic pregnancy
- If measurements subthreshold: Schedule repeat scan in 7-14 days—do not diagnose EPL prematurely
- Document cardiac activity with M-mode when CRL <7 mm to establish viability
Key caveat: Even with optimal ultrasound technique, a small proportion of ectopic pregnancies may be misclassified as missed abortion, particularly when adnexal mass or free fluid are absent 5, 4. Maintain clinical suspicion and ensure appropriate β-hCG follow-up when diagnosis uncertain.