A pregnant patient with prosthetic valve should be switched to heparin (from warfarin) at -

Ans. is 'b' i.e., 36 weeks a) In pregnancy warfarin should be replaced by heparin prior to conception and continued throughout the first trimester (In early pregnancy , warfarin damages organogenesis in fetus). b) After the first trimester heparin should he replaced by warfarin and continued upto term (continued exposure to heparin cause osteoporosis). c) Warfarin should be discontinued near term and heparin can be substituted at this stage (warfarin exacerbates neonatal hypoprothrombinemia and its control is too imprecise to be safe in labour where as heparin can be discontiuned just before labour and its anticoagulant effect wears off in about 6 hrs).