Sarah Lurvey, DO | EM PGY3
The Idea:
The stakes are high in this assessment because a false positive diagnosis of a nonviable pregnancy means termination of a viable pregnancy, which is more detrimental than a false negative in which case a diagnosis of a nonviable pregnancy is delayed likely by only a few days, assuming this is a hemodynamically stable patient who is being followed medically. The criteria therefore need a specificity of as close to 100% as possible.
Diagnosing a nonviable pregnancy involves physicians in many levels of training across many specialties, making widely used criteria difficult to establish, and current criteria are the product of only small studies.
The Study:
A review of the existing studies to differentiate diagnostic criteria for a nonviable pregnancy to establish criteria that near 100% specificity for nonviable pregnancy as opposed to merely suspicious for nonviable pregnancy. This includes a review of the use of hCG and pelvic ultrasonography in women with an IUP of uncertain viability or pregnancy of unknown location.
Inclusion criteria for these tests are a positive serum pregnancy test with a positivity threshold over 5mIU/ml, and a trans-vaginal assessment of the uterus, adnexa, evaluation for free fluid or a mass high in the pelvis which must be performed by physicians or providers overseen by credentialed physicians and images reviewed by US credentialed physicians, using equipment that can adequately see structures in the first trimester of pregnancy.
The Findings:
Trans-vaginal US Findings Diagnostic for Pregnancy Failure in IUP of Uncertain Viability:
Crown rump length ≥7mm and no heartbeat
Mean sac diameter of ≥25mm and no embryo
Absence of embryo heartbeat ≥2 weeks after a scan with a gestational sac without a yolk sac
Absence of embryo heartbeat ≥11 days after a scan with a gestational sac and yolk sac
Ruling out a viable IUP in a woman with a pregnancy of unknown location:
With ultrasonography demonstrating no intrauterine collection and normal adnexa:
hCG ≥3000 without anything visualized on US is most likely a nonviable IUP rather than an ectopic pregnancy, it’s generally appropriate to get one more hCG and US before terminating this pregnancy.
Anything less than hCG 3000 could very well be a viable IUP, do not take action. No single measurement of hCG can differentiate between ectopic and IUP, viable or not.
The Takeaway: hCG of ectopic pregnancies is extremely variable, often <1000, and hCG levels are not predictive of ectopic pregnancy rupture. Therefore in a woman with a positive hCG and clinical suspicion of ectopic pregnancy—trans-vaginal ultrasonography is always indicated.