What is the appropriate next step in management for a patient at 36 weeks of gestation with a prosthetic valve replacement for mitral stenosis on warfarin (anticoagulant) therapy with an International Normalized Ratio (INR) of 3?

Management at 36 Weeks Gestation with Prosthetic Valve on Warfarin

Discontinue warfarin immediately and initiate continuous intravenous unfractionated heparin (UFH) to prepare for delivery within the next 2-4 weeks. 1

Critical Action Required Now

At 36 weeks gestation, this patient has reached the critical transition point where warfarin must be stopped to prevent fetal and neonatal hemorrhagic complications during delivery. 1

Immediate Steps

• Stop warfarin today and begin continuous intravenous UFH with target aPTT at least 2 times control 1
• The current INR of 3.0 is appropriate for mechanical mitral valves (target range 2.5-3.5), but warfarin crosses the placenta and poses severe bleeding risk to the fetus during delivery 1
• ACC/AHA guidelines explicitly state warfarin should be discontinued 2-3 weeks before planned delivery, and at 36 weeks, delivery planning should begin 1

Rationale for UFH Over Other Options

Continuous intravenous UFH is the only acceptable anticoagulant at this gestational age because: 1

• UFH does not cross the placenta, eliminating fetal anticoagulation and hemorrhage risk 1
• UFH has a short half-life (60-90 minutes), allowing rapid reversal with protamine if emergency delivery or bleeding occurs 1
• LMWH is contraindicated this close to delivery due to inability to rapidly reverse and lack of reliable monitoring 1

Monitoring Requirements

• Maintain aPTT at least 2 times control (typically 60-80 seconds) 1
• Check aPTT every 4-6 hours initially until stable therapeutic range achieved 1
• Consider adding low-dose aspirin 75-100 mg daily if not already on it, as this is reasonable in second and third trimesters 1

Delivery Planning

Plan delivery between 37-39 weeks with the following protocol: 1

• Stop UFH infusion 4-6 hours before planned delivery (cesarean or vaginal) 1
• Resume UFH 4-6 hours after delivery if no significant bleeding 1
• Restart warfarin on postpartum day 1 if hemostasis is adequate 1
• Warfarin is safe during breastfeeding 2

Critical Pitfalls to Avoid

Never continue warfarin beyond 36 weeks - The risk of catastrophic fetal intracranial hemorrhage during labor and delivery is unacceptably high, with warfarin causing anticoagulation in the fetus that cannot be rapidly reversed. 1

Never use LMWH at this stage - Even with anti-Xa monitoring, LMWH cannot be rapidly reversed and has been associated with maternal valve thrombosis deaths when used inappropriately. 1 The FDA specifically warns against LMWH in pregnant women with mechanical valves without meticulous anti-Xa monitoring, and at 36 weeks, the delivery window is too narrow for safe LMWH use. 1

Never delay this transition - Maternal valve thrombosis risk increases if anticoagulation is interrupted, but this risk is lower than fetal death from hemorrhage if warfarin continues. 1 Three cases of maternal valve thrombosis have been reported in the literature when anticoagulation was inadequately managed. 3, 4

Maternal Risk Acknowledgment

While UFH carries higher maternal risks than warfarin (including valve thrombosis risk of approximately 5-9% vs. 5.7% with warfarin throughout pregnancy), at 36 weeks the fetal risks of continuing warfarin are prohibitive. 1 The guidelines universally recommend this transition despite the maternal risk because delivery is imminent and fetal safety becomes paramount. 1