A patient at 22 weeks pregnancy is on warfarin for oral anticoagulation for a known cardiac condition. Heparin is re-introduced at what gestation?

Heparin is given in first trimester to ease the mother from deep vein thrombosis but it cannot be continued as an injection after 12 weeks. After 12 weeks of gestation, oral warfarin tablets are given; if the warfarin is given before 12 weeks then warfarin related anomalies can happen to the fetus. Around 36 weeks, warfarin is stopped and we should resta heparin because continuing warfarin leads to increased bleeding during delivery.