First Trimester OB US
Abbreviations:
IUP: Intrauterine Pregnancy; EP: Ectopic Pregnancy; CRL: Crown Rump Length; MSD: Mean Gestational Sac Diameter; GS: Gestational Sac; YS: Yolk Sac; LMP: Last Menstrual Period
| Classification | Description | Notes |
| IUP of unknown viability: US suspicious, but not diagnostic of IUP failure | CRL < 7mm
MSD 16 – 24 mm, no embryo No heartbeat 2 weeks after US with GS but no YS No heartbeat 7 – 10 days after US with GS and YS Empty amnion (YS, no embryo) No embryo ≥ 6 weeks after LMP Yolk sac > 7 mm Sustained bradycardia (<80 bpm) Small gestational sac (MSD – CRL < 5 mm) |
Recommend: follow-up US in 7-10 days in stable patient |
| IUP of unknown viability: US diagnostic of IUP failure | CRL ≥ 7mm and no heartbeat
MSD ≥25 mm and no embryo No YS, embryo ≥ 2 weeks after US with GS but no YS No embryo ≥ 11 days after US with GS and YS |
|
| Pregnancy of Unknown Location | Intrauterine sac-like structure, no YS or embryo, normal adnexa | Most likely IUP, however, EP cannot be ruled out. |
| No intrauterine fluid collection, normal adnexa
1. hCG ≥ 3000: Viable IUP unlikely 2. most EP have hCG <3000, often <1000, but variable and does not predict rupture |
Recommend: 7 – 10 day f/u US and serial hCG |
References:
Doubilet, P. M., et al. (2013). “Diagnostic criteria for nonviable pregnancy early in the first trimester.” N Engl J Med 369(15): 1443-1451.
Lane BF, Wong-You-Cheong JJ, Javitt MC, et al. (2103). “ACR appropriateness criteria® First trimester bleeding.” Ultrasound Quarterly 29:91-96.