Tocolytics and Antenatal Corticosteroids

Learning objectives

After completing this chapter, you should be able to explain the limited goal of acute tocolysis; identify when labor should not be suppressed; compare nifedipine, indomethacin, and terbutaline; distinguish magnesium neuroprotection from tocolysis; describe antenatal betamethasone and dexamethasone regimens; manage late-preterm and repeat-course decisions; anticipate maternal and fetal adverse effects; and continue therapy safely during transport.

Opening transport scenario

A 25-year-old patient at 29 weeks has regular contractions and cervical change. Membranes are intact, fetal status is reassuring, and no infection or bleeding is present. The sending clinician orders betamethasone, magnesium for fetal neuroprotection, and nifedipine to gain time for transfer to a tertiary center. The transport team must understand that each medication has a different purpose and that no medication guarantees labor will stop.

1. Purpose and limits of tocolysis

Acute tocolysis may delay birth for approximately 48 hours to allow antenatal corticosteroids, maternal transfer, magnesium neuroprotection, or other time-limited interventions. It has not been shown to eliminate the underlying cause of preterm labor or reliably improve outcomes through prolonged maintenance therapy.

2. Is the patient a candidate?

Before administering or continuing a tocolytic, confirm gestational age, cervical change, membrane status, fetal status, maternal stability, placental concerns, infection risk, and the reason delay is desired. Tocolysis is generally considered before 34 weeks when a short delay is expected to provide meaningful benefit.

Common reasons not to suppress labor

• Intrauterine fetal demise or a lethal fetal condition.
• Nonreassuring fetal status requiring delivery.
• Severe preeclampsia or eclampsia requiring delivery.
• Maternal bleeding with hemodynamic instability or significant placental abruption.
• Chorioamnionitis or another condition in which delivery is the treatment.
• Advanced labor or imminent birth when delay is unrealistic.
• Agent-specific maternal contraindication or serious adverse effect.

With preterm prelabor rupture of membranes, routine tocolysis is controversial and infection changes the risk-benefit balance. In selected patients without infection or other contraindications, a brief course may be considered specifically for transport or corticosteroid administration according to obstetric direction.

3. Nifedipine for acute tocolysis

Nifedipine reduces calcium entry into uterine smooth muscle. It is commonly used because it is oral, effective for short-term delay, and generally well tolerated. Regimens vary; a common approach uses an oral loading dose followed by scheduled doses for up to 48 hours.

4. Indomethacin

Indomethacin inhibits prostaglandin synthesis and can be effective for early preterm labor, particularly before 32 weeks. Use is generally limited to a short course because fetal risks increase with gestational age and duration.

5. Terbutaline

Terbutaline is a beta-2 agonist that may be used as a short, monitored intervention for acute uterine tachysystole or selected preterm-labor situations. A common acute dose is 0.25 mg subcutaneously. The FDA warns against prolonged or maintenance use because serious maternal cardiovascular events and deaths have occurred.

• Monitor pulse, rhythm, BP, respiratory status, glucose, and potassium when clinically indicated.
• Adverse effects include tremor, palpitations, tachycardia, dysrhythmia, hyperglycemia, hypokalemia, myocardial ischemia, and pulmonary edema.
• Do not use oral terbutaline for treatment or prevention of preterm labor.
• Do not continue subcutaneous terbutaline beyond 48–72 hours, and acute obstetric use should occur in a monitored setting under direct obstetric oversight.

6. Magnesium is not the routine tocolytic

Magnesium sulfate may be present in the same preterm-labor patient for fetal neuroprotection, seizure prophylaxis, or eclampsia treatment. Its presence does not mean that it is being used to stop contractions, and the transport team should state the indication clearly during handoff.

7. Antenatal corticosteroids

Antenatal corticosteroids accelerate fetal maturation and reduce neonatal respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, and neonatal death when birth occurs within the effective window. Betamethasone and dexamethasone cross the placenta in active form.

Who is generally considered?

• A single course is recommended for patients 24 0/7 through 33 6/7 weeks at risk of delivery within 7 days, including selected patients with ruptured membranes and multifetal gestation.
• At 22 0/7 through 22 6/7 weeks, corticosteroids may be considered after counseling when neonatal resuscitation and intensive care are planned.
• For selected patients 34 0/7 through 36 6/7 weeks at risk of delivery within 7 days who have not received a prior course, late-preterm betamethasone may be considered.
• A medically indicated delivery should not be delayed solely to complete corticosteroids.

8. Repeat or rescue course

A single repeat course may be considered for a patient under 34 weeks who remains at risk of delivery within 7 days and whose prior course was more than 14 days earlier. In selected clinical situations, a repeat course may be considered as early as 7 days after the prior course. Regularly scheduled serial courses are not recommended.

9. Maternal effects and diabetes considerations

Corticosteroids can cause transient maternal hyperglycemia, often beginning within hours and lasting several days. Patients with diabetes may require intensified glucose monitoring and insulin adjustment. Hyperglycemia should not be mistaken for a reason to withhold a clearly indicated course without specialist discussion, but diabetic ketoacidosis, infection, and maternal instability require active management.

10. Transport implementation

• State the separate indication for every medication: contraction suppression, fetal maturation, fetal neuroprotection, infection treatment, or seizure prevention.
• Verify cervical findings, membrane status, fetal status, bleeding, infection signs, BP, pulse, respiratory status, glucose risk, and gestational age.
• Document each dose and due time; carry enough medication and pump power for the planned mission plus contingency.
• Reassess contractions, maternal adverse effects, fetal status, and whether the patient remains appropriate for transport.
• Stop or escalate for hypotension, chest pain, dysrhythmia, pulmonary edema, significant bleeding, infection, nonreassuring fetal status, or imminent birth.

11. Evolving case study

Phase 1: Building the plan

The patient at 29 weeks has cervical change without bleeding, infection, severe hypertension, or fetal compromise. Betamethasone is given for fetal maturation, magnesium is started for neuroprotection, and nifedipine is ordered to gain transfer time.

Phase 2: En route

After nifedipine, BP falls from 116/72 to 92/56 mm Hg and the patient becomes dizzy. The team repositions her, reassesses fetal status, confirms that no dose was duplicated, notifies medical direction, and holds further doses pending instruction.

Phase 3: Reframing the goal

Contractions continue but remain less frequent. The team does not promise that labor has stopped. The successful outcome is arrival at a center capable of neonatal care after initiation of time-sensitive fetal therapies.

12. High-yield chapter summary

1. Tocolysis buys time; it does not cure preterm labor.
2. The main goals are corticosteroid exposure, transfer, and magnesium neuroprotection when indicated.
3. Do not suppress labor when delivery is safer for the mother or fetus.
4. Nifedipine can cause hypotension and requires BP monitoring.
5. Indomethacin is generally limited to early gestation and short duration because of fetal ductal and renal effects.
6. Terbutaline can cause serious cardiovascular toxicity and is not for prolonged maintenance therapy.
7. Magnesium in preterm labor is usually for neuroprotection—not routine contraction suppression.
8. Betamethasone is 12 mg IM twice 24 hours apart; dexamethasone is 6 mg IM four times 12 hours apart.
9. Corticosteroid selection depends on gestational age, likelihood of delivery within 7 days, prior course, and neonatal plan.
10. Do not delay a medically indicated delivery to complete corticosteroids.

References

1. International Board of Specialty Certification. Maternal Fetal Transport Microcredential Candidate Handbook. Updated April 2026.
2. American College of Obstetricians and Gynecologists. Preterm Labor and Birth.
3. American College of Obstetricians and Gynecologists. Antenatal Corticosteroid Therapy for Fetal Maturation.
4. American College of Obstetricians and Gynecologists; Society for Maternal-Fetal Medicine. Use of Antenatal Corticosteroids at 22 Weeks of Gestation.
5. U.S. Food and Drug Administration. Drug Safety Communication: New Warnings Against Use of Terbutaline to Treat Preterm Labor.
6. Society for Maternal-Fetal Medicine. Management of Previable and Periviable Preterm Prelabor Rupture of Membranes. Consult Series #71.