The "Warfarin Window" in Pregnancy: The Importance of Half-life

Asnat Walfisch, Gideon Koren

Research output: Contribution to journalArticlepeer-review

28 Scopus citations

Abstract

Anticoagulation therapy during pregnancy in women with prosthetic cardiac valves is a therapeutic challenge. The use of vitamin K antagonists such as warfarin during pregnancy carries the potential for serious risks to the fetus, especially if these drugs are administered during the first trimester or at term. Between 6 and 12 weeks' gestation, fetal synthesis of proteins crucial for bone and cartilage formation may be impaired by warfarin, resulting in the well-defined "warfarin embryopathy." One of the most commonly suggested regimens involves the substitution of heparin for warfarin between 6 and 12 weeks' gestation to minimize the risk of warfarin embryopathy. Warfarin has a long half-life; following a single dose, the terminal elimination half-life is about one week, with a mean effective half-life of 40 hours. To date, all existing guidelines have ignored this long elimination half-life. If a policy of substituting heparin for warfarin between 6 and 12 weeks' gestation is followed, we suggest that substitution should begin at a much earlier gestational age. Substitution starting at 6 weeks' gestation may be too late to avoid embryopathy.

Original languageEnglish
Pages (from-to)988-989
Number of pages2
JournalJournal of Obstetrics and Gynaecology Canada
Volume32
Issue number10
DOIs
StatePublished - 1 Jan 2010
Externally publishedYes

Keywords

  • Anticoagulation
  • Pregnancy
  • Prosthetic valve
  • Warfarin
  • Warfarin embryopathy

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