Intrauterine Pregnancy of Uncertain Viability
The most likely diagnosis is D. Intrauterine pregnancy of uncertain viability (IPUV). At 5 weeks gestation with an intrauterine gestational sac but no visible embryonic cardiac activity, this presentation is entirely consistent with a normal early pregnancy that is too early to definitively assess viability 1.
Diagnostic Reasoning
At 5 weeks gestation, the absence of an embryo or cardiac activity is expected in a completely normal pregnancy. The yolk sac—the first definitive marker of intrauterine pregnancy—typically becomes visible only when the gestational sac exceeds 8 mm in mean sac diameter 1. The embryo and cardiac activity appear even later in normal development 1.
Why the Other Options Are Incorrect
Inevitable miscarriage (A) is ruled out because this diagnosis requires an open cervical os with vaginal bleeding, indicating that pregnancy loss is actively in progress 1, 2. This patient has a closed cervical os and no bleeding 1.
Threatened miscarriage (B) is excluded because this diagnosis requires vaginal bleeding with a closed cervical os in the presence of a viable intrauterine pregnancy 1, 2. This patient has no bleeding and viability has not yet been established 1.
Pregnancy of unknown location (C) is incorrect because the ultrasound clearly demonstrates an intrauterine gestational sac 3, 1. The Society of Radiologists in Ultrasound 2024 consensus explicitly states that PUL requires no evidence of probable or definite intrauterine or ectopic pregnancy 3. An empty gestational sac is considered a probable pregnancy and should not be termed a PUL 3.
Critical Management Principles
Management decisions must never be based on a single ultrasound at this early gestational age, as this risks harm to a normal pregnancy 1. The American College of Radiology emphasizes that at 5 weeks, it is too early to diagnose pregnancy loss based on a single ultrasound 1.
Required Follow-Up
Repeat transvaginal ultrasound in 7-14 days to assess for the appearance of a yolk sac, embryo, and cardiac activity 1.
Serial β-hCG measurements can help differentiate viable from nonviable pregnancy if diagnosis remains uncertain 4, 5. In viable intrauterine pregnancy, β-hCG typically doubles every 48-72 hours 6.
Definitive Diagnostic Criteria for Pregnancy Loss
The Society of Radiologists in Ultrasound 2024 consensus establishes that pregnancy loss can only be diagnosed when 3, 1:
- Crown-rump length ≥7 mm without cardiac activity, OR
- Mean sac diameter ≥25 mm without an embryo, OR
- Absence of embryo ≥14 days after initial visualization of gestational sac
None of these criteria are met in this case 3, 1.
Common Pitfalls to Avoid
Do not diagnose pregnancy loss based solely on the absence of cardiac activity at 5 weeks, as this is expected in normal pregnancies at this early stage 1.
Guard against injury to normal pregnancies by avoiding overinterpretation of a single early ultrasound 1, 7. Conservative diagnostic guidelines exist specifically to balance the risk of interrupting a viable pregnancy against the anxiety of delayed diagnosis 7.
Do not use a single hCG level to guide management in the absence of definitive ultrasound findings; serial measurements are required 1, 6.