Alteplase is a category C drug; there is very little evidence of its use in pregnancy. The major complication is of alteplase is bleeding, a risk which is increased by pregnancy. Therefore, the drug should only be used in pregnant woman when the potential risk of fetal harm is outweighed by the potential benefit of its use. The drug has not been determined to be safe for use during pregnancy and the drug has shown risk in animal models, so it is not in category A or B. It has also not been proven that the risks of alteplase use in pregnant women outweighs the benefits, so it is not in pregnancy category X.