Evaluation and Management of Anembryonic Pregnancy
An anembryonic pregnancy (also called embryonic demise or missed abortion) requires transvaginal ultrasound for definitive diagnosis, followed by active evacuation via medical or surgical management—expectant management is contraindicated due to increased risks of infection, hemorrhage, and coagulopathy. 1
Definitive Diagnostic Criteria
The diagnosis of anembryonic pregnancy is confirmed when transvaginal ultrasound demonstrates a mean gestational sac diameter (MSD) ≥25 mm without a visible embryo. 1 This threshold provides 100% certainty and eliminates the risk of misdiagnosing a viable early pregnancy. 1
Additional definitive criteria include:
- Crown-rump length (CRL) ≥7 mm without cardiac activity confirms embryonic demise with absolute certainty 1
- Absence of embryo with cardiac activity ≥14 days after initial visualization of a gestational sac without yolk sac 1
- Absence of embryo with cardiac activity ≥11 days after initial visualization of a gestational sac with yolk sac 1
Critical Pitfall: Premature Diagnosis
Never diagnose embryonic demise based on a single measurement if the CRL is <7 mm, even if cardiac activity is absent. 1 Research demonstrates that embryos measuring 2-4 mm without cardiac activity can progress to normal pregnancies. 2 When the gestational sac is <25 mm without an embryo, schedule repeat transvaginal ultrasound in 7-10 days rather than making an immediate diagnosis of pregnancy loss. 3, 1
Initial Evaluation Algorithm
1. Obtain Quantitative Serum β-hCG
Serial β-hCG measurements provide critical context, though they cannot diagnose anembryonic pregnancy alone. 3 In failing pregnancies, the mean hCG level is typically around 329 mIU/mL, significantly lower than in viable intrauterine pregnancies. 3
Obtain repeat serum β-hCG in exactly 48 hours to assess for appropriate rise or fall. 3 A viable early intrauterine pregnancy typically shows 53-66% rise over 48 hours, while nonviable pregnancies fail to rise appropriately or decrease. 3
2. Perform Transvaginal Ultrasound Immediately
Transvaginal ultrasound is the reference standard and must be performed regardless of β-hCG level. 3 The traditional discriminatory threshold of 3,000 mIU/mL has virtually no diagnostic utility (positive likelihood ratio 0.8, negative likelihood ratio 1.1) and should not delay imaging. 3
Document the following measurements precisely:
- Mean sac diameter (MSD): Average of three perpendicular diameters 1
- Presence or absence of yolk sac: Normally visible when MSD >8 mm 3, 4
- Presence or absence of embryo: Typically visible when MSD ≥16 mm 3, 4
- Crown-rump length if embryo present: Measured along the longest axis 1
- Cardiac activity: Document presence/absence and heart rate if present 1
Management Options After Confirmed Diagnosis
Expectant management is absolutely contraindicated in anembryonic pregnancy due to significantly increased maternal morbidity (60.2% vs 33.0% with active management), intraamniotic infection (38.0% vs 13.0%), and postpartum hemorrhage (23.1% vs 11.0%). 5 Active evacuation via medical or surgical methods must be offered. 1, 5
Medical Management
For gestational age <9 weeks, mifepristone 200 mg orally followed by misoprostol 800 mcg vaginally/buccally achieves approximately 80% success rate and is more effective than misoprostol alone. 5 This combination is particularly effective for anembryonic pregnancy. 5
Misoprostol alone (600-800 mcg vaginally) has a 91.5% success rate in the first trimester but carries higher bleeding and infection risks compared to surgical management. 5
Surgical Management
Vacuum aspiration (manual or electric) is the procedure of choice and has the lowest complication rates: hemorrhage 9.1%, infection 1.3%, retained tissue requiring repeat procedure 1.3%. 5 This compares favorably to medical management: hemorrhage 28.3%, infection 23.9%, retained tissue 17.4%. 5
For gestational age 9-12 weeks, surgical evacuation is preferred. 5 For gestational age >12 weeks, dilation and evacuation (D&E) is the procedure of choice. 5
Essential Preventive Measures
Rh Immunoprophylaxis
All Rh-negative women with anembryonic pregnancy must receive 50 μg anti-D immunoglobulin to prevent alloimmunization. 1, 5 Fetomaternal hemorrhage occurs in approximately 32% of spontaneous abortions. 5 This must be administered regardless of whether management is medical or surgical. 5
Infection Recognition and Management
Clinical symptoms of infection may be subtle at early gestational ages. 5 Do not wait for fever to diagnose intrauterine infection. 5 Warning signs requiring immediate action include:
- Maternal tachycardia 5
- Purulent cervical discharge 5
- Uterine tenderness 5
- Fetal tachycardia (if embryo present) 5
If infection is suspected, initiate broad-spectrum antibiotics immediately and proceed with urgent surgical evacuation without waiting for confirmatory tests. 5
Follow-Up and Contraceptive Counseling
After complete evacuation, provide contraceptive counseling immediately, as ovulation can resume within 2-4 weeks post-abortion. 5 Combined hormonal contraceptives or implants can be initiated immediately without waiting for next menses. 5 If starting contraception within 7 days of abortion, no backup contraception is needed. 5
Serial β-hCG measurements should continue until levels reach zero to confirm complete resolution and exclude gestational trophoblastic disease. 3
Terminology Recommendations
Use "anembryonic pregnancy," "embryonic demise," or "early pregnancy loss (EPL)" rather than outdated terms like "blighted ovum," "missed abortion," or "nonviable pregnancy." 1, 5 When gestational age is ≥11 weeks, use the term "fetal demise" instead of "embryonic demise." 1, 5