UW Emergency Radiology

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.