This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
[{'content': 'A prosthetic valve patient switch to heparin at which time of pregnancy: \nSelect and explain. \nA. 28 weeks, B. 32 weeks, C. 36 weeks, D. Postpartum', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Pregnancy following valve replacement:\nMechanical valve replacement is not preferred these days as anticoagulation is required throughout pregnancy.\nProblem of anticoagulation: During pregnancy, the main problem is of anticoagulation. Warfarin is safe for the mother but can result in warfarin embryopathy of the fetus, miscarriage, IUGR and stillbirths. Heparin is safe for the fetus as it does not cross the placenta, but is less effective than warfarin in preventing thromboembolic events. Low molecular weight heparin is inadequate and ACOG does not recommend its use in pregnant women with prosthetic\xa0heart valves.', 'role': 'assistant'}]