Anticoagulation
Direct oral anticoagulants, so far, are prohibited in pregnancy as there
is little information on maternal and fetal safety. The choice between
therapeutic anticoagulation with low molecular weight heparin (LMWH) or
vitamin K antagonist (VKA) is made according to the stage of pregnancy.
Warfarin, a VKA, crosses the placenta and can cause fetal bleeding,
including intracranial hemorrhage, and increase fetal anomalies, with
the latter occurring mainly during the first trimester. Neither
unfractionated heparin nor LMWH crosses the placenta, so these agents do
not cause fetal bleeding or teratogenicity, although bleeding at the
uteroplacental junction and fetal wastage are possible. Therefore,
heparins are recommended for anticoagulation in the first trimester,
being replaced by VKA after that. Women receiving VKA should be changed
to either LMWH or unfractionated heparin after 36 weeks of gestation to
reduce the risk of fetal hemorrhage at the time of vaginal delivery as
well as delivery-associated maternal bleeding.