Anembryonic Pregnancy (Blighted Ovum)

Definition

• Mean gestational sac diameter (MSD) > 25 mm with no embryonic pole present (per current conservative diagnostic criteria), OR
• MSD between 16 and 45 mm without evidence of a fetal pole (per broader clinical definitions)

• Berek & Novak's Gynecology, p. 1750
• Swanson's Family Medicine Review, p. 431

Pathophysiology / Etiology

• Embryo simply fails to develop after fertilization; the trophoblast implants and the gestational sac grows, but no embryo forms
• The most common underlying cause is de novo fetal aneuploidy - at least 60% of preclinical and early clinical pregnancy losses result from chromosomal abnormalities
• Anembryonic losses are particularly thought to arise from fetal aneuploidy (in contrast to losses after 10 weeks, which are less commonly aneuploid)
• The most common single chromosomal abnormality seen is monosomy X (45,X), especially among anembryonic conceptuses
• Berek & Novak's Gynecology, p. 1792-1793

Epidemiology

• 8-20% of known pregnancies end in spontaneous abortion; ~80% of these occur in the first trimester
• Risk factors include: increasing maternal age, prior spontaneous abortion, maternal diabetes, maternal smoking, closely spaced pregnancies, extremes of maternal weight, uterine anomalies, thrombophilic states

Diagnosis

Ultrasound Criteria (TVUS - gold standard)

Important: These are conservative criteria designed to avoid intervening in a potentially viable pregnancy. Clinical judgment and patient wishes must always be incorporated. Serial ultrasound may be needed before a definitive diagnosis.

Biochemical Support

• Serum β-hCG should normally double every ~48 hours in viable pregnancy; a rise < 50% suggests an abnormal pregnancy
• A change < 15% (plateau) is most predictive of ectopic pregnancy
• Low serum progesterone (< 15 ng/mL) or estradiol (< 200 ng/mL) indicates a blighted ovum with ~90% likelihood
• Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 794

Classification within Spontaneous Abortion Types

Management

1. Expectant Management

• Success rate for anembryonic pregnancies: ~66% (lower than incomplete abortion at 91%, or missed abortion at 76%)
• May take 4-8 weeks for the pregnancy to pass spontaneously
• Associated with increased unscheduled surgical evacuations and bleeding, but no increase in infection rates
• Acceptable in stable, counseled patients who prefer to avoid intervention

2. Medical Management (Misoprostol)

• 800 mcg vaginally is the ACOG-recommended dose; efficacy up to 84% in achieving complete abortion
• Sublingual route: 600 mcg is acceptable
• Women with anembryonic pregnancy require a second dose of misoprostol more often than women with incomplete/inevitable abortions
• Mifepristone 200 mg oral given 24 hours before misoprostol improves success: ~83% success with pre-treatment vs. ~67% with misoprostol alone

3. Surgical Management (Suction Curettage / Manual Vacuum Aspiration)

• Indicated for:
  • Patient preference
  • Excessive bleeding or hemodynamic instability
  • Concern about reliable follow-up
• Can be performed safely in outpatient setting under local anesthesia

Additional Considerations

• Check blood type and Rh status
• Give Rho(D) immune globulin (RhoGAM) if Rh-negative (50 mcg up to 12 weeks; 300 mcg dose if smaller dose unavailable)
• Thrombophilia (e.g., antiphospholipid syndrome) is unlikely to be the cause of anembryonic or early biochemical losses, and treatment is unlikely to alter outcome in this specific category
• Berek & Novak's Gynecology, p. 1750-1753
• Swanson's Family Medicine Review, p. 431-432

Prognosis and Counseling

• Even with recurrent pregnancy loss (3+ losses), a patient is more likely to carry her next pregnancy to term than to miscarry
• Risk of subsequent loss after 2 recognized losses: ~24%; after 3 losses: ~30%; after 4 losses: 40-50%
• Patients should be reassured that in most cases, spontaneous abortion does not recur
• If recurrent pregnancy loss is being investigated, workup can begin after 2 consecutive losses
• Chromosomal karyotyping of both partners (G-banding), uterine cavity evaluation, and APS antibody testing are key investigations

Summary: Anembryonic pregnancy is a gestational sac without an embryo, confirmed on TVUS (MSD > 25 mm, no embryonic pole). It results most often from fetal aneuploidy. Management is patient-centered: expectant (66% success), medical (misoprostol ± mifepristone, ~83-84% success), or surgical. Rh status must be checked and RhoGAM given as needed.