Which trimester of pregnancy is Warfarin contraindicated?

Warfarin is contraindicated during the first trimester of pregnancy due to its known teratogenic effects. During this early stage of fetal development, critical organ systems are forming, and exposure to Warfarin can lead to significant developmental issues, including fetal warfarin syndrome. This syndrome can manifest with a variety of birth defects such as skeletal dysplasia, facial abnormalities, and central nervous system complications.

Although Warfarin continues to pose risks in later trimesters, the highest risk of major congenital malformations occurs when it is administered during the first trimester. The use of Warfarin is generally avoided throughout pregnancy, but it is particularly important to avoid it during the first trimester because of the potential for critical harm during the earliest stages of fetal development when the foundations for organogenesis are being laid down. Doctors often use alternative anticoagulants that are safer for use during pregnancy to manage thromboembolic risks, especially in women who are pregnant or planning to become pregnant.