Anticoagulants are used during pregnancy to prevent venous thrombo-emb
olism in high-risk patients, to prevent systemic embolism in patients
with prosthetic heart valves or native valvular heart disease, and to
treat patients with acute venous thrombo-embolism. Neither unfractiona
ted nor low-molecular-weight heparin cross the placenta and both appea
r to be safe for the fetus, Oral anticoagulants do cross the placenta
and they have been associated with the development of warfarin embryop
athy, central nervous system anomalies, and fetal haemorrhage. The tru
e incidence of these events is not known. Both heparin and oral antico
agulants can be safely administered to nursing mothers.