New SBAs on Sarcoidosis in Pregnancy

A 30 year old woman is seen in the Maternal Medicine pre-conception clinic.  She is known to have pulmonary sarcoidosis with a diagnosis of interstitial lung disease (ILD), as well as a history of previous lupus pernio.  Her sarcoidosis has been well controlled for the last four years, with low dose prednisolone, azathioprine and methotrexate.  Her last respiratory function testing showed an FVC of 1.4L.  What is the most appropriate next investigation?