Advice: scan them. The risk to both the patient and the foetus is far greater from the cord compression than from the MR scan. Also this must be taken in context: if the only other alternative is an (ionising) x-ray investigation, then MRI is definitely preferable.
Note that the question is phrased "what would you advise...". This is not accidental; the responsibility for the management of the patient lies with the clinician, and the decision to scan them must lie with them. (They have the medical knowledge to weigh the pros and cons getting—or not getting—the information the MRI scan would provide.) You are, of course, responsible for the advice you give.