USMLE Prep - Medical Reference Library

Preterm Labor — Tocolytics, Steroids, and MgSO₄

System: Obstetrics Gynecology • Reviewed: Aug 31, 2025 • Step 1Step 2Step 3

Synopsis:

Diagnose preterm labor clinically; use antenatal corticosteroids and magnesium sulfate for neuroprotection; tocolytics for short‑term pregnancy prolongation to allow steroid/transfer window.

Key Points

  • Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
  • Use system-specific risk tools to guide testing and disposition.
  • Order high-yield tests first; escalate imaging when indicated.
  • Start evidence-based initial therapy and reassess frequently.

Algorithm

  1. Primary survey and vitals; IV access and monitors.
  2. Focused history/physical; identify red flags and likely etiologies.
  3. Order system-appropriate labs and imaging (see Investigations).
  4. Initiate guideline-based empiric therapy (see Pharmacology).
  5. Reassess response; arrange consultation and definitive management.

Clinical Synopsis & Reasoning

For Preterm Labor Tocolytics Steroids And Mgso, frame the differential by acuity and pathophysiology, then align diagnostics to the leading hypotheses. Prioritize stabilization while obtaining high‑yield studies such as CBC (Baseline hematology), BMP (Electrolytes/renal). Incorporate bedside imaging and targeted labs to define severity and identify complications; synthesize results with clinical trajectory to refine the working diagnosis and disposition needs.


Treatment Strategy & Disposition

Initiate disease‑directed therapy alongside supportive care, titrating to objective response. Pharmacologic options commonly include Analgesia/Antipyretics. Use validated frameworks (e.g., Tocolytic Selection) to guide escalation and site of care. Address precipitating factors, de‑escalate empiric therapies with data, and arrange follow‑up for monitoring and risk‑factor modification; admit patients with instability, high risk of deterioration, or needs for close monitoring.


Management Notes

Avoid maintenance tocolysis. Monitor for maternal side effects (hypotension with nifedipine).


Epidemiology / Risk Factors

  • Risk factors vary by condition and patient profile

Investigations

TestRole / RationaleTypical FindingsNotes
CBCBaseline hematologyAbnormal counts
BMPElectrolytes/renalDerangements

Tocolytic Selection

GAAgent/Notes
<32 wksIndomethacin (avoid with ductal constriction risk), or nifedipine
32–34 wksNifedipine preferred
ContraindicationsIU infection, abruption, fetal demise, severe preeclampsia
AdjunctsHydration, rest not curative
Rescue steroidsConsider per protocol

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
AcetaminophenAnalgesic/antipyreticHoursSymptom control as appropriateHepatotoxicity (overdose)
Ondansetron5-HT3 antagonismMinutesAntiemesis if neededQT prolongation

Prognosis / Complications

  • Prognosis depends on severity, comorbidities, and timeliness of care

Patient Education / Counseling

  • Explain red flags and when to seek emergent care.
  • Reinforce medication adherence and follow-up plan.

References

  1. ACOG Preterm Labor — Link