Dexamethasone Rescue Dose in Pregnancy
A rescue course of antenatal corticosteroids in pregnancy should be a single course of betamethasone or dexamethasone (typically 12 mg IM every 24 hours for 2 doses or 6 mg IM every 12 hours for 4 doses) administered to women less than 34 0/7 weeks gestation who remain at high risk of preterm delivery and whose initial course was given more than 14 days prior, though rescue dosing may be considered as early as 7 days after the prior course if clinically indicated. 1, 2
Critical Context: Rescue vs. Initial Course
The term "rescue dose" in obstetrics specifically refers to a repeat course of antenatal corticosteroids given when delivery has not occurred after the initial course and the patient remains at risk of preterm birth. This is distinct from:
- Initial course: First administration for fetal lung maturation 1
- Maternal indications: Treatment of maternal disease (where dexamethasone should generally be avoided) 3
- Fetal cardiac indications: Treatment of fetal heart block (4 mg daily oral dexamethasone) 4
Rescue Course Dosing Algorithm
Eligibility Criteria
- Gestational age: Less than 34 0/7 weeks 1, 2
- Risk assessment: Imminent risk of preterm delivery within 7 days 1, 2
- Timing from initial course: At least 14 days since prior course (optimal), though may be given as early as 7 days if clinical scenario warrants 1, 2, 5
Standard Rescue Dosing Regimens
Option 1 (Betamethasone - preferred):
- 12 mg intramuscularly every 24 hours for 2 doses 1
Option 2 (Dexamethasone):
Recent evidence suggests 5 mg dexamethasone every 12 hours for 4 doses may be noninferior to 6 mg dosing for late preterm births (32-36 weeks), though this requires further validation 6.
Important Caveats and Pitfalls
Do Not Give Multiple Rescue Courses
- Only a single repeat course should be administered 1, 2
- Repeated courses beyond one rescue dose are associated with reduced infant birthweight and head circumference 4
- The immunosuppressive and neurodevelopmental risks of multiple courses outweigh benefits 6
Timing Considerations
- The 7-day minimum interval is a clinical judgment call for urgent situations 1, 2
- The 14-day interval represents optimal timing for rescue dosing 1, 2
- Do not administer after 34 0/7 weeks for rescue purposes (different criteria apply for late preterm 34-36 weeks initial course) 1
Route of Administration
- Intramuscular administration is standard for antenatal corticosteroids for fetal lung maturation 1, 2
- This differs from maternal indications where oral or IV routes may be used 4, 7
Avoid Confusion with Other Pregnancy Indications
Do NOT use rescue course dosing for:
- Maternal disease control (use prednisone/prednisolone instead) 3
- Fetal heart block (use 4 mg oral dexamethasone daily, limited duration) 4
- Postoperative nausea/vomiting (8 mg single dose) 4, 7
- Pre-eclampsia acceleration of fetal lung maturity at ≥34 weeks (different indication and timing) 4
Safety Profile
Maternal Safety
- Single rescue course has acceptable safety profile 1, 2
- Fluorinated corticosteroids (dexamethasone, betamethasone) cross the placenta extensively, which is the intended mechanism for fetal lung maturation 4, 3
- Risk of maternal hyperglycemia, hypertension, and infection should be monitored 4
Fetal/Neonatal Safety
- Reduces respiratory distress syndrome, intraventricular hemorrhage, and necrotizing enterocolitis 1, 8
- Optimal gestational age for maximum benefit is 31-34 weeks 8
- Concerns about neurodevelopmental effects with multiple courses necessitate limiting to single rescue dose 6
Clinical Decision Framework
If patient received initial course >14 days ago and <34 weeks:
- Assess imminent delivery risk (within 7 days)
- If high risk: Administer single rescue course 1, 2
- If low risk: Observe and reassess
If patient received initial course 7-14 days ago and <34 weeks:
- Consider rescue course only if clinical scenario indicates imminent delivery 1, 2
- Weigh urgency against optimal 14-day interval
If patient is ≥34 weeks: