What is the role of terbutaline (beta-2 adrenergic agonist) in managing nonreassuring fetal status due to contractions during labor?

Terbutaline for Nonreassuring Fetal Status Due to Contractions

Terbutaline is an appropriate and effective tocolytic agent for acute intrauterine resuscitation when nonreassuring fetal heart rate patterns are associated with excessive uterine contractions, provided there are no contraindications such as maternal cardiovascular disease, tachycardia >100 bpm, thyrotoxicosis, or severe placental abruption. 1

Mechanism and Rationale

• Terbutaline transiently stops uterine contractions, allowing fetal metabolic recovery by improving uteroplacental blood flow and reducing oxygen demand during periods of fetal distress 1, 2
• Tocolytic agents like terbutaline improve fetal heart rate tracings compared with untreated controls, though improvements in neonatal outcomes have not been definitively demonstrated 1
• The primary goal is to stabilize the fetus temporarily while preparing for expedited delivery if needed, or to allow continuation of labor if the fetal status improves 2

Administration Protocol

• The standard dose is 0.25 mg (250 micrograms) administered as an intravenous bolus 3, 4, 5
• Alternative route: subcutaneous administration at the same dose 6, 7
• Onset of action is rapid, with uterine activity inhibition occurring within minutes and lasting approximately 15-60 minutes 5
• Terbutaline provides more effective tocolysis with lower contraction frequency (median 2.9 vs 4 per 10 minutes) compared to nitroglycerin 4

Expected Maternal Effects

• Maternal tachycardia is common but generally well-tolerated, occurring in most patients 3, 5
• Unlike nitroglycerin, terbutaline does not significantly decrease maternal mean arterial pressure (82 to 81 mm Hg), maintaining better maternal hemodynamic stability 4
• Systemic beta-2 agonist administration may cause maternal hyperglycemia and metabolic effects 1
• Potential for neonatal hypoglycemia exists as a result of maternal administration 6, 7

Contraindications and Safety Considerations

Absolute contraindications include: 3

• Maternal cardiovascular disease
• Maternal tachycardia >100 beats/min at baseline
• Thyrotoxicosis
• Fluid overload or pulmonary edema risk
• Concurrent corticosteroid or atropine use
• Severe placental abruption

Critical safety warnings from FDA labeling: 6, 7

• Terbutaline should NOT be used for prolonged tocolysis beyond 48-72 hours
• Serious adverse reactions including maternal death have been reported with prolonged use
• Maternal risks with extended use include cardiac arrhythmias, pulmonary edema, and myocardial ischemia
• Increased fetal heart rate may occur

Clinical Outcomes and Efficacy

• In properly selected patients, terbutaline achieved successful acute intrauterine resuscitation in 71.9% of cases with nonreassuring fetal heart rate patterns 4
• Fetal heart rate tracings and pH improved in 89% (32/36) of treated patients in one study 3
• Electronic monitoring demonstrated evidence of partial or total fetal recovery after therapy in all 15 patients in another series 2
• Neonatal outcomes were favorable, with 10/15 patients having initial Apgar scores ≥7, and all achieving scores ≥7 by 5 minutes 2

Integration into Intrauterine Resuscitation Algorithm

When nonreassuring fetal status is identified, follow this sequence: 1

1. Maternal repositioning (lateral position to optimize uterine blood flow)
2. Oxygen administration to the mother
3. IV fluid bolus if hypotension present
4. Discontinue oxytocin if being administered
5. Consider amnioinfusion for recurrent variable decelerations
6. Administer terbutaline 0.25 mg IV if excessive uterine activity persists and no contraindications exist
7. Continuous fetal monitoring to assess response
8. Prepare for expedited delivery (operative vaginal or cesarean) if fetal status does not improve

Fetal Monitoring After Administration

• Continue continuous electronic fetal monitoring to assess response to therapy 1
• Improvement in fetal heart rate variability and resolution of decelerations indicates successful resuscitation 3, 2
• If delivery is imminent, even severe decelerations are less significant than in earlier stages of labor 1
• Persistent nonreassuring patterns despite terbutaline warrant proceeding to cesarean delivery 2

Common Pitfalls to Avoid

• Do not use terbutaline as a substitute for timely delivery when indicated - it is a temporizing measure only 1
• Avoid administration in patients with contraindications, as serious maternal complications can occur 3
• Do not confuse acute intrapartum use (appropriate) with prolonged tocolysis for preterm labor prevention (contraindicated) 6, 7
• Terbutaline may have a tocolytic effect during delivery itself, which should be considered when timing administration 1
• Monitor for tachysystole reduction (terbutaline reduces tachysystole to 1.8% vs 18.9% with nitroglycerin) 4