Skip to Main Content

++

  • Defined as delivery before completion of 37 weeks
  • Increasing in frequency in the United States: 9.4% (1981), 10.7% (1992), 12.3% (2003), 12.8% (2006)
  • Pathophysiology:
    • Excessive myometrial and fetal membrane overdistention:
      • Multiple gestation
      • Polyhydramnios
    • Decidual hemorrhage
    • Precocious fetal endocrine activity
    • Intrauterine infection or inflammation
  • Clinical diagnosis: regular, painful uterine contractions + cervical dilatation or effacement
  • Outcome:
    • Thirty percent diagnosed as “preterm labor” will deliver full term
    • Fifty percent hospitalized for “preterm labor” will deliver full term
    • Therapeutic interventions seldom effective in prolonging pregnancy

++

  • Most tocolytic drugs are only effective to prolong pregnancy for 24–48 hours
  • Delay delivery to allow corticosteroid (betamethasone) delivery and effect to mature pulmonary surfactant:
    • Typical dose 12 mg IM once daily (two doses total)
    • Initial benefit at 18 hours after first dose
    • Maximum benefit at 48 hours of therapy
    • Decrease risk of neonatal respiratory distress, intraventricular hemorrhage, necrotizing enterocolitis, and perinatal death
  • Permit transport of mother to regional facility

++

See following table.

++
Table Graphic Jump Location
Favorite Table | Download (.pdf) | Print
Tocolytic Agents
MedicationMechanismEfficacySide effects
Beta-2 agonists (terbutaline, ritodrine)
  • Beta-2 stimulation inhibits myosin light chain kinase via a G-protein-coupled increase in intracellular cAMP
  • Bolus dose of terbutaline is 250 μg IV push; this achieves uterine relaxation for a few minutes duration
  • For suppression of preterm labor an infusion is started at 2.5 μg/min and increased by 2.5 μg/min every 20 min until the contractions stopped; maximum rate is 25 μg/min
  • Ritodrine is no longer available in the United States
  • Decrease immediate (within 48 h) birth rate
  • No decrease in delivery rates at 7 days
  • No change in perinatal or neonatal mortality
  • Hypotension due to beta-2-mediated vasodilation
  • Tachycardia, atrial fibrillation/flutter
  • Myocardial ischemia
  • Pulmonary edema
  • Hyperglycemia secondary to glucagon-mediated glycogenolysis and gluconeogenesis
  • Hypokalemia/rebound hyperkalemia (intracellular transfer)
  • Increased fetal heart rate
  • Fetal hypoglycemia
Calcium channel blockers (nifedipine)
  • L-type calcium channel inhibition reduces intracellular calcium levels in uterine smooth muscle
  • Nifedipine is the most commonly used agent
  • Usual starting oral dose is 10–20 mg
  • Repeat dosing and frequency is less clear
    • High doses have been associated with pulmonary edema
  • Reduce delivery rates within 7 days of treatment
  • Reduce frequency of neonatal respiratory distress, intraventricular hemorrhage, necrotizing enterocolitis, and neonatal jaundice
  • Pulmonary edema (possible high-output heart failure?)
  • Hypotension
  • Fetal death
  • Heart block
  • Neuromuscular block in combination with magnesium sulfate therapy
Magnesium sulfate
  • Mechanism of action is poorly understood
  • Decreases the frequency of depolarization of muscle by modulating calcium uptake, binding, and distribution
  • High concentrations needed for effect
  • Loading dose is 6 g (as opposed to 4 g in preeclampsia) and infusion of 2 g/h for maintenance
  • No difference in the risk of birth within 48 h
  • No difference in perinatal mortality compared with placebo
  • May have neuroprotective effects in newborn if administered to mother prior to preterm birth
  • Nausea, vomiting, and lethargy
  • Volume overload
  • Shortness of breath
  • Pulmonary edema
  • Chest pain
  • Respiratory arrest
  • Cardiac arrest
  • Neonatal paralytic ileus
  • Interference with neuromuscular monitoring
  • Enhances effects ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessAnesthesiology Full Site: One-Year Subscription

Connect to the full suite of AccessAnesthesiology content and resources including procedural videos, interactive self-assessment, real-life cases, 20+ textbooks, and more

$995 USD
Buy Now

Pay Per View: Timed Access to all of AccessAnesthesiology

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.