What are the effects of warfarin and superwarfarin toxicity during pregnancy?

Updated: Jan 19, 2018
  • Author: Kent R Olson, MD, FACEP; Chief Editor: David Vearrier, MD, MPH  more...
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Warfarin crosses the placenta during pregnancy and has the potential to cause teratogenesis and bleeding in the fetus. Warfarin and other coumarin derivatives cause an embryopathy commonly termed fetal warfarin syndrome (FWS). No data are available on whether superwarfarin compounds cross the placenta or are excreted in breast milk.

During the first trimester, particularly during weeks 6-12 of gestation, embryopathy caused by exposure and characterized by nasal hypoplasia with or without stippled epiphyses (chondrodysplasia punctata) may occur.

Central nervous system (CNS) abnormalities, including dorsal midline dysplasia characterized by agenesis of the corpus callosum, Dandy-Walker malformation, and midline cerebellar atrophy have been reported.

Ventral midline dysplasia, characterized by optic atrophy and eye abnormalities, has been observed. Seizures, deafness, blindness, and mental retardation can occur in any trimester. Spontaneous fetal abortion and stillbirth are known to occur, and an increased risk of fetal mortality is associated with warfarin use.

Although rare, other teratogenic occurrences reported after in utero exposure to warfarin include the following:

  • Urinary tract abnormalities (eg, single kidney)
  • Asplenia
  • Anencephaly
  • Spina bifida
  • Cranial nerve palsy
  • Hydrocephalus
  • Cardiac defects and congenital heart disease
  • Polydactyly
  • Deformities of toes
  • Diaphragmatic hernia
  • Corneal leukoma
  • Cleft palate
  • Cleft lip
  • Schizencephaly
  • Microcephaly

The effects of anticoagulation on the fetus are a particular concern during labor, when the combination of the trauma of delivery and anticoagulation may lead to bleeding in the neonate.

A few small studies have looked at the use warfarin in pregnancy after the 12th week of gestation, but these studies are insufficient to recommend the use of warfarin in the pregnant patient. Thus, do not administer warfarin during pregnancy.

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