What is the next test to confirm the diagnosis of a blighted ovum?

Confirming the Diagnosis of Anembryonic Pregnancy (Blighted Ovum)

The next test to confirm the diagnosis is a repeat transvaginal ultrasound in 7-10 days, combined with serial quantitative serum β-hCG measurements 48 hours apart. 1

Why a Single Ultrasound Is Insufficient

A single ultrasound showing an empty gestational sac is never adequate for definitive diagnosis of anembryonic pregnancy, as this could represent either a nonviable pregnancy or simply incorrect dating in a viable early pregnancy. 1, 2 The most critical pitfall to avoid is initiating treatment based on one ultrasound with size-dates discrepancy—this could result in termination of a viable pregnancy with uncertain last menstrual period. 1

Diagnostic Algorithm

Step 1: Obtain baseline quantitative serum β-hCG

• Establish a reference point for comparison 1

Step 2: Repeat β-hCG in exactly 48 hours

• If β-hCG doubles appropriately → likely viable pregnancy with incorrect dating; repeat ultrasound in 7-10 days 1
• If β-hCG plateaus or rises inadequately → suspect abnormal pregnancy; obtain specialty consultation 1
• If β-hCG declines → confirms nonviable pregnancy; proceed to management options 1

Step 3: Repeat transvaginal ultrasound in 7-10 days

• This allows sufficient time for embryonic development to become visible if pregnancy is viable 1, 2

Definitive Diagnostic Criteria

Anembryonic pregnancy can only be diagnosed when one of these ultrasound criteria is met: 3, 4, 1

• Mean gestational sac diameter ≥25 mm without an embryo
• Absence of embryo ≥14 days after initial visualization of gestational sac without yolk sac
• Absence of embryo with cardiac activity ≥11 days after visualization of yolk sac

The outdated term "blighted ovum" should be replaced with "anembryonic pregnancy" or "diagnostic of early pregnancy loss (EPL)" in all documentation. 3, 4

Critical Timing Considerations

Never use β-hCG discriminatory thresholds alone to make management decisions without ultrasound correlation—serial measurements are essential, as single β-hCG values have limited diagnostic utility. 1 Many patients have irregular cycles or uncertain last menstrual period, making dating unreliable. 1

When to Expedite Intervention

Immediate evaluation and possible intervention are required if the patient develops: 1

• Severe abdominal pain
• Heavy vaginal bleeding with hemodynamic instability
• Signs of infection (fever, purulent discharge, uterine tenderness)
• Peritoneal signs on examination