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Heparin does not cross the placenta and has no effect on the foetus.
Oral anticoagulants cross the placenta and have been associated with an increased abortion rate in the first trimester. There may also be an association with foetal cerebral haemorrhage when given within a few days of vaginal delivery.
NSAIDS and salicylates may prolong gestation and labour, and result in premature closure of the ductus arteriosus. Also, they may be associated with neonatal hypertension and haemorrhage.