Definitive Nonviable IUP — Single Exam (SRU 2012)
These criteria carry ~100% specificity for nonviability — diagnosis can be made without a follow-up scan:
| Finding | Threshold (TVUS) | Diagnosis |
|---|---|---|
| No cardiac activity | CRL ≥7 mm | Embryonic/fetal demise |
| No embryo (anembryonic) | MSD ≥25 mm | Anembryonic pregnancy |
| No embryo with cardiac activity | ≥11 days after prior US showing sac + yolk sac | Nonviable IUP (sequential scans) |
| No embryo with cardiac activity | ≥14 days after prior US showing sac without yolk sac | Nonviable IUP (sequential scans) |
| Empty amnion | Amnion visible without adjacent embryo | Highly suspicious — confirm on repeat |
Do NOT diagnose nonviability based on thresholds below these cutoffs. Repeat TVUS in 7–14 days is required for findings in the "suspicious but not diagnostic" range. False-positive diagnosis of nonviability leads to termination of viable pregnancies.
Suspicious but Not Diagnostic — Follow-Up Required
| Finding | Threshold | Action |
|---|---|---|
| No cardiac activity | CRL <7 mm | Repeat TVUS in 7–14 days |
| No embryo visible | MSD 16–24 mm | Repeat TVUS in 7–14 days |
| Small sac sign | MSD − CRL <5 mm | Poor prognosis; repeat in 7–10 days |
| Slow fetal heart rate | FHR <100 bpm at <6.3 wks; <120 bpm at 6.3–7 wks | Repeat in 7–10 days; do not diagnose nonviability on rate alone |
| Large yolk sac | >7 mm | Poor prognostic sign; follow-up in 7–10 days |
Normal Developmental Milestones (TVUS)
| Structure | When Visible | Notes |
|---|---|---|
| Gestational sac (GS) | ~4.5–5.0 wks GA; β-hCG ~1,000–1,500 mIU/mL | Growth ~1.1 mm/day; intradecidual sign → double decidual sac sign → true GS with echogenic ring |
| Yolk sac | ~5.5 wks GA; MSD ≥10 mm | Normal ≤7 mm; >7 mm = poor prognostic sign; absence when MSD ≥10 mm = suspicious |
| Embryo | ~6.0 wks GA; MSD ≥16 mm | Must be present when MSD ≥25 mm; absent at MSD ≥25 mm = anembryonic |
| Cardiac activity | ~6.0–6.5 wks GA; CRL ≥2–3 mm | Consistently present by CRL 7 mm; absent at CRL ≥7 mm = nonviable |
Fetal Heart Rate by Gestational Age
| Gestational Age | Normal FHR | Significance |
|---|---|---|
| 6.0–6.2 weeks | 100–134 bpm | <100 bpm = poor prognosis; repeat in 7–10 days |
| 6.3–7.0 weeks | 120–154 bpm | <120 bpm = poor prognosis |
| 7.1–8.0 weeks | ≥110 bpm minimum | <110 bpm = high likelihood of demise |
| 8.0–10.0 weeks | 137–170 bpm | Peaks ~9–10 weeks then gradually declines toward term |
Pregnancy of Unknown Location (PUL)
PUL = positive pregnancy test without IUP or ectopic on initial TVUS. Manage with serial hCG and progesterone until definitive diagnosis.
| Parameter | Value | Interpretation |
|---|---|---|
| Progesterone | <5 ng/mL | Nonviable gestation (IUP or ectopic); 98.2% PPV for failed PUL at ≤3.2 ng/mL |
| Progesterone | 5–20 ng/mL | Indeterminate; ectopic possible |
| Progesterone | >20 ng/mL | Likely viable IUP |
| 48h hCG rise | ≥35% increase | Consistent with viable IUP; serial TVUS when above discriminatory zone |
| 48h hCG fall | >13% decrease | Failed PUL (92.7% sensitivity, 96.7% specificity) |
| hCG plateau | <15% change over 48h | Ectopic or persistent PUL — consider MTX or surgery if hCG >2,000 |
PUL outcomes: ~50–70% failed PUL · ~30–47% IUP · ~6–20% ectopic · ~2% persistent PUL. Ectopic is the critical minority — manage all PUL with serial hCG + TVUS until definitive diagnosis.
References
Doubilet PM et al. Diagnostic Criteria for Nonviable Pregnancy Early in the First Trimester. NEJM. 2013;369(15):1443–51.
Rodgers SK et al. First-Trimester US: What Does Normal Look Like? RadioGraphics. 2015;35(5):1445–56.