What is the initial recommendation for tocolysis in preterm labour?

Initial Tocolytic Therapy for Preterm Labor

For women in preterm labor between 24-34 weeks gestation, tocolytic therapy is recommended primarily to delay delivery for 48-72 hours to allow for administration of antenatal corticosteroids and maternal transfer to a tertiary care facility with appropriate neonatal intensive care capabilities. 1

First-Line Tocolytic Options

• Nifedipine is recommended as a reasonable first-line tocolytic agent due to its effectiveness in delaying delivery, favorable side effect profile compared to beta-mimetics, and association with improved neonatal outcomes 2, 3
• Initial dosing regimen: 10 mg nifedipine capsules orally every 15 minutes up to 40 mg in the first hour, followed by 20 mg slow-release nifedipine at 90 minutes 4
• Calcium channel blockers like nifedipine have been shown to decrease adverse neonatal outcomes by significantly delaying delivery and are associated with fewer maternal side effects than beta-mimetics 2, 3

Alternative Tocolytic Options

• Indomethacin may be considered as a reasonable first choice for acute tocolysis in gestational ages less than 32 weeks, but prolonged use (>48 hours) should be avoided 2
• Atosiban (oxytocin receptor antagonist) has an excellent maternal and fetal safety profile but has not been shown to significantly reduce neonatal complications 2, 5
• When compared with calcium channel blockers, atosiban results in fewer maternal adverse effects but may be less effective at prolonging gestation 3

Magnesium Sulfate Considerations

• While magnesium sulfate is sometimes used as a tocolytic, evidence for its effectiveness is controversial 2, 6
• Its primary benefit in the periviable period is for fetal neuroprotection, reducing the incidence of cerebral palsy when administered before anticipated early preterm birth 1
• Important safety considerations with magnesium sulfate include:
  • Monitoring for signs of magnesium toxicity (loss of deep tendon reflexes, respiratory depression) 7
  • Caution in patients with renal impairment as magnesium is eliminated by the kidneys 7
  • Continuous administration beyond 5-7 days can lead to fetal hypocalcemia and bone abnormalities 7

Duration and Limitations of Tocolysis

• Tocolytic therapy generally does not significantly lengthen gestational age beyond seven days 2
• Despite the ability to delay delivery temporarily, no tocolytic has been consistently shown to improve overall neonatal outcomes or reduce the overall rate of preterm birth 1
• The primary benefit remains gaining time for corticosteroid administration and maternal transfer to appropriate facilities 1

Clinical Monitoring During Tocolysis

• For magnesium sulfate: monitor deep tendon reflexes, respiratory rate (should remain ≥16 breaths/min), urine output (maintain at ≥100 mL over 4 hours), and serum magnesium levels 7
• For nifedipine: monitor maternal blood pressure and heart rate due to potential hypotensive effects, though these are less severe than with beta-mimetics 3
• Continuous fetal monitoring should be maintained during acute tocolysis 1

Contraindications to Tocolysis

• Tocolytic therapy is generally not recommended when delivery would be beneficial for maternal or fetal indications 1
• Specific contraindications include severe preeclampsia, chorioamnionitis, fetal distress, or significant maternal hemorrhage 1