Table 2.

Recommendations²⁰ for anticogulation during pregnancy in patients with mechanical prosthetic valves: weeks 1–35

Indication	Class
1. The decision whether to use heparin during the first trimester or to continue oral anticoagulation throughout pregnancy should be made after full discussion with the patient and her partner; if she chooses to change to heparin for the first trimester, she should be made aware that heparin is less safe for her, with a higher risk of both thrombosis and bleeding, and that any risk to the mother also jeopardises the baby*	I
2. High risk women (a history of thromboembolism or an older generation mechanical prosthesis in the mitral position) who choose not to take warfarin during the first trimester should receive continuous unfractionated heparin intravenously in a dose to prolong the midinterval (6 hours after dosing) aPTT to 2–3 times control. Transition to warfarin can occur thereafter	I
3. In patients receiving warfarin, INR should be maintained between 2.0–3.0 with the lowest possible dose of warfarin, and low dose aspirin should be added	IIa
4. Women at low risk (no history of thromboembolism, newer low profile prosthesis) may be managed with adjusted dose subcutaneous heparin (17 500–20 000 U twice daily) to prolong the mid interval (6 hours after dosing) aPTT to 2–3 times control.	IIb

Class I There is evidence and/or general agreement that a given procedure or treatment is useful and effective.

Class IIa Weight of evidence/opinion is in favour of usefulness/efficacy.

Class IIb Usefulness/efficacy is less well established by evidence/opinion.

From the European Society of Cardiology guidelines for prevention of thromboembolic events in valvular heart disease.²⁰

aPPT, activated partial prothrombin time; INR, international normalised ratio.