A pregnant patient with prosthetic valve should be switched to heparin in -

36 weeks There are different views on administration of warfarin during pregnancy :- i) According to one group warfarin cause significant adverse teratogenic effects and should be avoided in pregnancy. ii) Some believe that warfarin produces teratogenic effect only during 1si and 3rd trimester and can be safely given during 2nd trimester. iii) The third group opines that warfarin embryopathy develops only after exposure to oral anticoagulant during the first trimester of pregnancy. As a consequence warfarin is contraindicated in the first 6-12 weeks of pregnancy. Warfarin can be administered after this period. But they also add that - Warfarin should be replaced by heparin before the anticipated date of delivery as :? - Warfarin produces anticoagulant effect in the fetus that can cause bleeding. This is of paicular concern at deliver), when trauma to the head during passage through the bih canal can lead to intracranial bleeding. - Warfarin is a long acting drug while heparin is a sho acting drug, so, the action of heparin, can be terminated rapidly prior to the bih.