What is the recommended dose of vaginal progesterone (micronized progesterone) for a short cervix?

Vaginal Progesterone Dosing for Short Cervix

For patients with a short cervix (≤20 mm) identified before 24 weeks of gestation, either 200 mg micronized progesterone capsules or 90 mg (8%) progesterone gel administered vaginally daily are recommended formulations, as there are insufficient data to recommend one specific formulation or dose over the other. 1

Evidence-Based Recommendations for Short Cervix Management

Defining Short Cervix

• Short cervix is defined as a transvaginal cervical length ≤25 mm in mid-trimester (typically measured between 18-24 weeks gestation)
• Patients with cervical length ≤20 mm have the strongest evidence for benefit from progesterone therapy
• Patients with cervical length 21-25 mm may also benefit, though evidence is less robust

Recommended Progesterone Formulations and Dosing

• Two formulations have been most extensively studied in clinical trials:
  • 200 mg micronized progesterone vaginal capsules daily 1, 2
  • 90 mg (8%) progesterone vaginal gel daily 1, 3
• Treatment should begin upon diagnosis of short cervix (before 24 weeks)
• Continue treatment until 36+6 weeks gestation, rupture of membranes, or delivery, whichever occurs first 3

Efficacy by Cervical Length

• For cervical length ≤20 mm:

  • Strong evidence supports vaginal progesterone use (GRADE 1A recommendation) 1
  • Reduces preterm birth <33 weeks by approximately 45% (RR 0.55; 95% CI 0.33-0.92) 3
  • Reduces neonatal morbidity including respiratory distress syndrome 3

• For cervical length 21-25 mm:

  • Moderate evidence supports consideration of vaginal progesterone (GRADE 1B recommendation) 1
  • Shared decision-making recommended 1
  • One study showed no significant benefit over bed rest for this specific cervical length range 4

Clinical Implementation

Patient Selection

• Asymptomatic singleton pregnancies
• Short cervix identified on transvaginal ultrasound before 24 weeks
• No history of preterm birth required (benefit seen even in nulliparous patients) 4

Monitoring

• No need to monitor serum progesterone levels, as vaginal progesterone in pregnancy produces only minimal changes in systemic levels 5
• Median increase in serum progesterone after vaginal administration is only about 24% over baseline pregnancy levels 5

Important Caveats

• Vaginal progesterone use for short cervix is currently off-label and requires patient counseling 1
• 17-alpha hydroxyprogesterone caproate (17-OHPC) should NOT be used for short cervix without history of preterm birth (FDA approval withdrawn in 2023) 1
• For patients with both short cervix AND history of preterm birth, either vaginal progesterone or 17-OHPC may be considered, though recent evidence suggests comparable efficacy 6
• Cerclage is generally not recommended for short cervix without history of preterm birth 1

Practical Considerations

• Patient preference may influence choice between gel and capsule formulations
• Insurance coverage and cost may vary between formulations
• Adherence to daily administration is important for efficacy
• Treatment should be initiated promptly upon diagnosis of short cervix

The Society for Maternal-Fetal Medicine (SMFM) explicitly states that there are insufficient data to recommend a specific formulation or dose for short cervix treatment, despite both 200 mg micronized progesterone capsules and 90 mg progesterone gel showing efficacy in clinical trials 1.