In pregnancy, how is Cushing's syndrome typically diagnosed?

• A. Imaging studies are used for diagnosis because lab cortisol levels may be unreliable during pregnancy
• B. Lab cortisol testing is definitive
• C. Urine cortisol is always unreliable
• D. Serum ACTH measurement alone confirms diagnosis

Answer: (A)

In pregnancy, cortisol physiology is altered enough that relying on lab tests alone to diagnose Cushing’s syndrome can be misleading. Total cortisol levels rise because of increased cortisol-binding globulin, and the interpretation of urine or serum cortisol becomes unreliable. Dexamethasone suppression testing and some other biochemical tests can also be affected by pregnancy changes, making it harder to confirm hypercortisolism biochemically. Because of these factors, imaging to locate and characterize the source of excess cortisol is used to establish the diagnosis. MRI is preferred during pregnancy (without gadolinium) to evaluate the pituitary and adrenal glands, while CT is avoided due to fetal radiation exposure. Thus, imaging studies provide the practical means to diagnose and guide management when lab values may be unreliable in pregnancy.