I had a high (for male bodies) prolactin level BEFORE starting HRT, 30-34. An MRI shows a 3.5 mm adenoma on the left side of the pituitary. This is probably what is called a microprolactinoma.
I haven't been pregnant recently... I'm being monitored with regular labs, and if the level rises significantly, I'll be given a drug that is well understood and safe, cabergoline, which blocks the signal to produce prolactin and shrinks prolactinomas. Up to 95% of these adenomas show no growth over a 4-6 year period (Schlechte J, Dolan K, Sherman B, et al. The natural history of untreated hyperprolactinemia: a prospective analysis. J Clin Endocrinol Metab. 1989 Feb. 68(2):412-8. [Medline])