Medication Principles in Pregnancy

Learning objectives

After completing this chapter, you should be able to explain pregnancy-related pharmacokinetic changes, describe placental transfer, use current medication-labeling information, balance medication and disease risks, and manage high-alert medications safely during transport.

Seven questions before giving or accepting a medication

1

Why?
Maternal, fetal, or combined indication.

2

Benefit?
What outcome should improve?

3

Risk?
Maternal, fetal, neonatal, and untreated-disease risk.

4

Dose?
Concentration, route, organ function, and timing.

5

Monitor?
Vitals, labs, fetal status, and therapeutic effect.

6

Rescue?
Antidote, airway plan, vasopressor, or stop criteria.

7

Handoff?
Last dose, response, next dose, and responsible clinician.

Opening transport scenario

A 32-week patient is being transferred with severe hypertension and threatened preterm birth. She is receiving magnesium sulfate, an antihypertensive, and antibiotics; betamethasone was given three hours earlier. The sending bag label, pump display, and written order list different magnesium concentrations. The most important pharmacology action is not memorizing a dose—it is stopping the transfer process long enough to reconcile the medication system.

1. Medication risk is not binary

The correct question is rarely “Is this drug safe?” A better question is: Does the expected benefit outweigh the known and uncertain risks for this patient at this time?

2. FDA pregnancy and lactation labeling

The former A, B, C, D, and X pregnancy categories are obsolete for prescription labeling. The Pregnancy and Lactation Labeling Rule uses narrative sections covering a risk summary, clinical considerations, and supporting data. Transport clinicians should review current prescribing information rather than relying on an old letter category copied into a protocol or reference app.

3. Pregnancy and ADME

4. Distribution and protein binding

Expanded plasma volume and total body water can increase the volume of distribution of hydrophilic drugs. Increased fat can alter distribution of lipophilic drugs. Lower albumin may increase the unbound fraction of highly protein-bound drugs, while increased clearance may offset the effect. A “low total level” does not always mean a low active free concentration.

5. Placental transfer

6. Timing and developmental risk

7. Clinical medication decision framework

8. Dosing, weight, renal, and hepatic function

Use the drug-specific dosing method in protocol or order. Some emergency medications use actual body weight; others use ideal, lean, or adjusted weight, a maximum dose, or a fixed regimen. Pregnancy-related weight gain is not a reason to invent a dosing method. Review renal and hepatic function because clearance and toxicity may change rapidly in preeclampsia, sepsis, hemorrhage, and critical illness.

9. High-alert infusions in transport

Before movement

• Read the original order and indication.
• Match bag label, pharmacy label, pump concentration, and dose/rate.
• Trace every line from container to patient.
• Confirm IV/IO patency and dedicated-line requirements.
• Check compatibility, battery, tubing volume, and remaining medication.
• Program alarms and identify stop criteria.
• Perform independent read-back for high-alert medications.

10. Compatibility, access, and interruption

Limited vascular access creates risk. Verify Y-site compatibility, flush requirements, lumen selection, carrier-fluid needs, and whether the medication can be paused. Plan for pump failure, line dislodgement, extravasation, or diversion. Some therapies require a dedicated line because interruption or incompatibility may cause immediate harm.

11. Medication reconciliation and handoff

Before transport

Home medications, allergies, last doses, recent changes, sending medications, and withheld therapies.

During transport

Time, dose/rate, indication, response, adverse effects, line changes, and rescue interventions.

Receiving handoff

Cumulative dose, remaining volume, next dose due, monitoring needs, and who assumes responsibility.

12. Patient communication and consent

Use plain language to explain the indication, expected benefit, common and serious adverse effects, uncertainty, alternatives, and the risk of withholding treatment. Avoid absolute statements such as “perfectly safe” or “always dangerous.” Document questions, refusal, consent when required, and the decision-making discussion.

13. Evolving case study

Phase 1: Medication discrepancy

The sending order, bag, and pump display list different magnesium concentrations. The transport team stops and resolves the discrepancy with the sending clinician and pharmacy before departure.

Phase 2: System verification

The team confirms the maternal indication, fetal-neuroprotection plan, infusion rate, urine output, reflexes, respiratory rate, calcium availability, and next laboratory check.

Phase 3: En-route change

Respiratory rate falls and reflexes become absent. The team stops the infusion, supports ventilation, activates the rescue plan, and communicates the change.

Phase 4: Handoff

The receiving team receives the exact concentration, cumulative dose, stop time, maternal response, fetal response, and rescue treatment. Responsibility is transferred at the bedside.

14. High-yield chapter summary

1. Medication risk must be compared with the risk of untreated disease.
2. FDA letter categories are obsolete; use current narrative labeling.
3. Pregnancy changes absorption, distribution, metabolism, and excretion in drug-specific ways.
4. Lower albumin can change free-drug fraction.
5. Increased GFR can increase clearance of selected drugs.
6. Do not apply one dose adjustment to every medication.
7. Placental transfer depends on molecular and placental factors.
8. Gestational timing changes the type of possible effect.
9. Know whether the indication is maternal, fetal, or both.
10. High-alert transport infusions require independent verification and line tracing.
11. Confirm compatibility, power, remaining volume, and rescue plans.
12. Medication reconciliation must include last dose, response, adverse effects, and next dose.
13. Avoid absolute safety claims when counseling patients.
14. Resolve discrepancies before movement.

References

1. International Board of Specialty Certification. Maternal Fetal Transport Microcredential Candidate Handbook. Updated April 2026.
2. U.S. Food and Drug Administration. Pregnancy and Lactation Labeling Final Rule.
3. U.S. Food and Drug Administration. Pregnancy and Lactation Medication Information for the Healthcare Provider.
4. Eke AC, et al. Physiologic changes during pregnancy and impact on drug disposition. 2023.
5. Pinheiro EA, et al. Drugs in pregnancy: pharmacologic and physiologic changes that affect clinical care. 2021.
6. Pariente G, et al. Pregnancy-associated changes in pharmacokinetics: a systematic review. PLoS Medicine. 2016.
7. Society for Maternal-Fetal Medicine. A Maternal Transport Briefing Form and Checklist. Reaffirmed 2025.