What is the best way to prevent preterm labor?

Best Methods for Preventing Preterm Labor

For women with a history of spontaneous preterm birth, 17-alpha-hydroxyprogesterone caproate (17P) 250 mg IM weekly from 16-20 weeks until 36 weeks is the recommended first-line therapy to prevent recurrent preterm birth. 1

Risk-Based Prevention Strategies

For Women with Prior Spontaneous Preterm Birth (SPTB)

• First-line therapy: 17P 250 mg IM weekly starting at 16-20 weeks until 36 weeks of gestation 1

  • This recommendation is based on strong evidence showing a 34% reduction in recurrent preterm birth at <37 weeks (from 54.9% to 36.3%) 1
  • Also reduces preterm birth at <32 weeks and <35 weeks, and significant reductions in infant complications (intraventricular hemorrhage, necrotizing enterocolitis, need for supplemental oxygen) 1

• Alternative if 17P unavailable: Vaginal progesterone may be considered, though evidence is less robust 1

  • Multiple trials have failed to show consistent benefit of vaginal progesterone in preventing recurrent preterm birth 1

For Women with Short Cervical Length (CL ≤20 mm) without Prior SPTB

• Recommended therapy: Vaginal progesterone 90-mg gel or 200-mg suppository daily from diagnosis until 36 weeks 1
  • Significantly reduces preterm birth <33 weeks (7.6% vs 15.3%) 1
  • Also reduces neonatal morbidity 1

For Women with Multiple Gestations

• No progesterone recommended: Multiple studies show no benefit of either 17P or vaginal progesterone in twin or triplet pregnancies 1
  • Several RCTs have consistently demonstrated lack of efficacy in this population

For Women with Threatened Preterm Labor or PPROM

• No progesterone recommended: Insufficient evidence to support use in these scenarios 1

Cervical Length Monitoring

• For women with prior SPTB receiving 17P:

  • If cervix shortens to <25 mm by 24 weeks, continue 17P 1
  • Consider cervical cerclage if cervical length <15 mm 1

• For women without prior SPTB:

  • Consider universal cervical length screening at 18-24 weeks 1
  • If CL ≤20 mm, initiate vaginal progesterone 1

Important Clinical Considerations

1. Timing matters: Progesterone therapy should begin early (16-20 weeks for 17P) and continue until 36-37 weeks 1

2. Route-specific efficacy: Do not substitute one form of progesterone for another as they have different efficacy profiles for different indications 1

3. Common pitfalls to avoid:

   • Using progesterone in multiple gestations (not effective) 1
   • Starting therapy too late (after 24 weeks may reduce efficacy) 1
   • Switching from 17P to vaginal progesterone if cervix shortens in women with prior SPTB (insufficient evidence) 1
   • Using progesterone for tocolysis in active preterm labor (not effective) 1

4. Quality control for cervical length measurement:

   • Transvaginal ultrasound should be performed with proper technique and quality control 1
   • Measurements should be taken at 18-24 weeks for screening purposes 1

The evidence strongly supports a risk-based approach to preterm birth prevention, with specific interventions tailored to specific risk factors. The most robust evidence supports 17P for women with prior spontaneous preterm birth and vaginal progesterone for women with short cervical length without prior preterm birth.