Anticoagulation in pregnacy

• Warfarin can cross placenta. Its use in the first trimester of pregnancy is associated with embryopathy characterized by nasal hypoplasia, stippled epiphysis or both. (Heparin does not cross placenta).
• LMWH has been associated with mechanical prosthetic valve thrombosis in prignant woman. The etiology is unknown, possible inadequate dosing during pregnancy.

Options of anticoagulation management in pregnancy with mechanical prosthetic valve.

1. Warfarin throughout pregnancy, with its potential fetal risks. Change to heparin (UFH or LMWH) at 38 weeks, Labor induction at 40 weeks of gestation.
2. Heparin throughout pregnancy, with its associated maternal thrombosis risks particularlly mechanical heart valve prosthesis. It is anticipated that heparin dose in the third trimester will be higher.
3. Heparin during the first trimester. Switch to warfarin in the second trimester. Change back to heparin at 38 weeks. Labor induction at 40 weeks of gestation. Heparin dose in the third trimester is usually higher.

For UFH, start with total daily dose of 35000 U given subcutaneously twice a day. Monitor PTT at least twice a week to keep the level at least 2-3 times of control.

For LMWH such as Lavenox, start with 100 mg given subcutaneously twice a day. Monitor anti-Xa to keep the level at 0.5 -1.2 U/ml 4-6 hours after innection.

Risk of mechanical heart valve prosthesis thrombosis in pregnancy continue to be high with heparin therapy. The heparin dose should be kept at high PTT or anti-Xa level, carefully.

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