What are the strategies for preventing preterm labor?

Preterm Labor Prevention

The most effective evidence-based strategies for preventing preterm birth are 17-alpha-hydroxyprogesterone caproate (250 mg IM weekly) for women with prior spontaneous preterm birth, and vaginal progesterone for women with short cervical length, while activity restriction should be avoided as it provides no benefit and may cause harm. 1, 2

Primary Prevention Strategies

Progesterone Therapy (First-Line Prevention)

For women with prior spontaneous preterm birth:

• Administer 17-alpha-hydroxyprogesterone caproate 250 mg intramuscularly weekly starting between 16-24 weeks of gestation until 37 weeks 1, 2
• This reduces preterm birth at <37 weeks from approximately 55% to 37% in high-risk women 2
• Continue weekly injections until delivery or 37 weeks gestation 2

For women with short cervical length (<25mm) on transvaginal ultrasound:

• Vaginal progesterone is recommended for singleton pregnancies with short cervix detected between 16-24 weeks 1
• Screen high-risk women with transvaginal ultrasound cervical length measurement between 16-24 weeks 3

Important limitations:

• Progestogens have no proven benefit for multiple gestations, active preterm labor, or preterm premature rupture of membranes 1
• Do not use progesterone as treatment once active labor has begun 1

Cervical Length Screening

• Perform transvaginal ultrasound cervical length measurement at 16-24 weeks in women with risk factors for preterm birth 3
• Cervical length <25mm identifies women who may benefit from progesterone therapy 3
• This is the most effective screening tool for identifying women at risk 3

What NOT to Do: Activity Restriction

Activity restriction and bed rest should NOT be recommended for preterm labor prevention:

• Randomized controlled trials show no benefit in preventing preterm birth 4
• Women prescribed activity restriction had higher rates of preterm delivery (37.1% vs 14.3%; adjusted OR 2.1) 4
• Activity restriction causes maternal harm including deconditioning, bone loss, and psychological stress 4
• Despite 80% of maternal-fetal medicine specialists historically using this intervention, the majority acknowledge no documented benefit 4

Management of Threatened Preterm Labor

GBS Prophylaxis Protocol

For women presenting with signs of preterm labor <37 weeks:

• Obtain vaginal-rectal swab for GBS culture immediately if no screen within preceding 5 weeks 4, 5
• Start GBS prophylaxis immediately while awaiting culture results 4, 5
• Use penicillin G 5 million units IV initially, then 2.5-3 million units IV every 4 hours until delivery 5
• If labor does not progress, discontinue GBS prophylaxis 4, 5
• If culture returns positive and labor resumes, restart prophylaxis 4, 5

Antibiotics for Preterm Premature Rupture of Membranes

• Administer antibiotics for latency prolongation and GBS prophylaxis in women with PPROM 4
• For PPROM at ≥24 weeks: antibiotics are recommended 4
• For PPROM at 20-23 6/7 weeks: antibiotics can be considered 4

Antenatal Corticosteroids

• Administer antenatal corticosteroids if delivery is anticipated and no prior course has been given 5
• This applies to gestational ages where neonatal resuscitation would be offered 4
• Do not administer corticosteroids in previable/periviable PPROM until the time when neonatal resuscitation would be appropriate 4

Magnesium Sulfate for Neuroprotection

• Administer magnesium sulfate for fetal neuroprotection when delivery is anticipated before 32 weeks 5
• This reduces the risk of cerebral palsy in surviving infants 5

Common Pitfalls to Avoid

Do not rely on oral antepartum antibiotics for GBS:

• Oral antibiotics do not eliminate GBS colonization and do not prevent neonatal disease 5
• Intrapartum prophylaxis is required regardless of antepartum treatment 5

Do not use tocolytics for long-term prevention:

• Tocolytics may delay delivery briefly (48 hours) but do not improve neonatal outcomes 5
• Use tocolytics only to allow time for corticosteroid administration and maternal transport 6, 3

Do not recommend activity restriction:

• This intervention is ineffective and potentially harmful 4
• Focus instead on evidence-based interventions like progesterone therapy 1, 2

Do not use cerclage, amnioinfusions, or amniopatch routinely:

• Serial amnioinfusions and amniopatch are investigational and should only be used in clinical trials 4
• Cerclage after PPROM requires individualized risk-benefit discussion 4

Risk Stratification

High-risk patients requiring intervention:

• Prior spontaneous preterm birth (progesterone indicated) 1, 2
• Short cervical length <25mm on ultrasound (progesterone indicated) 1, 3
• Multiple gestation (no proven preventive therapy available) 1
• Preterm labor symptoms with positive fetal fibronectin 3

Moderate-risk patients requiring surveillance:

• History of cervical procedures (LEEP, cone biopsy) 3
• Uterine anomalies 3
• Prior second-trimester loss 3