Check for existence of a field in a Microsoft Access table

I have a vba program that alters a linked table - a new field is added.  Before I create the field, I need to make sure that it doesn't already exist.  Here is the code I have to do the alter:

Public Function Alter_Table()
    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field
    Dim strSQL As String
   
    On Error GoTo Alter_Table_Exit
   
    Set db = DBEngine.OpenDatabase("C:\Quote Templates\Data Files\Quote Data.mdb")
    Set tdf = db.TableDefs("tbl_Quotes")
   
    Set fld = tdf.CreateField("Freight_PO", dbBoolean)
    fld.DefaultValue = 0
    tdf.Fields.Append fld
    Set fld = Nothing
   
    Set fld = tdf.CreateField("Freight_Amt", dbCurrency)
    fld.DefaultValue = 0
    tdf.Fields.Append fld
    Set fld = Nothing
    Set tdf = Nothing
   
    db.Close
    Set db = Nothing

    Set db = CurrentDb()
    Set tdf = db.TableDefs("tbl_Quotes")
    tdf.RefreshLink

Alter_Table_Exit:
   
    DoCmd.OpenQuery ("qupd_Freight_Amt_0")
     
    Set tdf = Nothing
    db.Close
    Set db = Nothing
    Exit Function
   
End Function