Should I start Duphaston (dydrogesterone) in a patient with a crown‑rump length less than 7 mm and no detectable fetal heartbeat?

No Duphaston (Dydrogesterone) – Observation Only

When the crown-rump length is less than 7 mm without detectable cardiac activity, you should NOT start Duphaston or any other progesterone supplementation; instead, schedule a repeat transvaginal ultrasound in 7–10 days to confirm viability or diagnose embryonic demise, because a CRL <7 mm is below the diagnostic threshold and may represent either a dating error or true early pregnancy loss. 1, 2

Why Progesterone Is Not Indicated

• Progesterone supplementation (including dydrogesterone) does not prevent miscarriage when embryonic demise has already occurred or is imminent. 3
• The absence of cardiac activity at CRL <7 mm is suggestive but not diagnostic of embryonic demise—approximately 8.3% of embryos measuring 4–5 mm CRL without cardiac activity will subsequently demonstrate viability on follow-up scanning. 2, 4
• Starting progesterone at this stage may delay recognition of a non-viable pregnancy and expose the patient to unnecessary medication without clinical benefit. 3

Diagnostic Approach for CRL <7 mm Without Cardiac Activity

Immediate Assessment

• Confirm the measurement technique: Ensure transvaginal ultrasound was used (not transabdominal) and that CRL was measured along the longest axis of the embryo. 1, 5
• Verify dating: Review the last menstrual period to exclude dating errors that could explain the absence of cardiac activity. 1, 5
• Document exact CRL measurement: Interobserver variability for CRL at this size can be ±14.64%, so precise documentation is critical. 6

Follow-Up Protocol

• Schedule repeat transvaginal ultrasound in 7–10 days to reassess for cardiac activity and measure interval growth. 1, 2
• Do NOT diagnose embryonic demise based on a single scan when CRL is <7 mm, even if cardiac activity is absent—this threshold exists specifically to avoid inadvertent termination of wanted pregnancies. 1, 2
• At the follow-up scan:
  • If CRL has grown to ≥7 mm without cardiac activity, embryonic demise is confirmed with 100% certainty. 1, 2
  • If cardiac activity is now present, the pregnancy is viable and progesterone may be considered only if there are other indications (e.g., history of recurrent pregnancy loss, threatened abortion with bleeding). 3

When Cardiac Activity Should Be Visible

• Cardiac activity is typically detectable by transvaginal ultrasound at approximately 6 weeks gestational age, with reliable visualization by 7 weeks in normal pregnancies. 7, 5
• At a CRL of 3.5–5.3 mm, the absence of cardiac activity has a positive predictive value approaching 100% for embryonic demise under ideal scanning conditions, but current consensus guidelines use the more conservative ≥7 mm threshold to minimize false-positive diagnoses. 1, 2, 4

Critical Pitfalls to Avoid

• Never start progesterone supplementation to "rescue" a pregnancy when viability is uncertain—this practice is not evidence-based and may obscure the diagnosis of embryonic demise. 3
• Do not use mean sac diameter (MSD) alone to make management decisions when an embryo is visible; CRL is the primary measurement for dating and viability assessment once an embryo is measurable. 1, 5
• Avoid the term "threatened abortion" in this scenario—the patient has an intrauterine pregnancy of uncertain viability (IPUV) that requires follow-up imaging, not immediate intervention. 3, 2

Management After Confirmed Embryonic Demise (CRL ≥7 mm Without Cardiac Activity)

If the repeat scan confirms embryonic demise:

• Offer active evacuation (medical or surgical) rather than expectant management, as expectant management is associated with significantly higher maternal morbidity (60.2% vs 33.0%), intraamniotic infection (38.0% vs 13.0%), and postpartum hemorrhage (23.1% vs 11.0%). 3, 1
• Surgical vacuum aspiration has the lowest complication rates: hemorrhage 9.1%, infection 1.3%, retained tissue 1.3%. 3
• Medical management with mifepristone 200 mg plus misoprostol 800 mcg achieves approximately 80% success rate for missed abortion. 3, 1
• Administer 50 μg anti-D immunoglobulin to all Rh-negative patients to prevent alloimmunization, as fetomaternal hemorrhage occurs in approximately 32% of spontaneous abortions. 3, 1

Summary Algorithm

1. CRL <7 mm without cardiac activity → Repeat transvaginal ultrasound in 7–10 days 1, 2
2. Do NOT start progesterone at this stage 3
3. At follow-up scan:
   • CRL ≥7 mm without cardiac activity → Diagnose embryonic demise, offer evacuation 1
   • Cardiac activity now present → Viable pregnancy, consider progesterone only if other indications exist 3, 5
   • CRL still <7 mm without cardiac activity → Repeat scan in another 7 days or measure serial β-hCG 3, 1