The patient should undergo formal visual field testing. During pregnancy, there is concern that prolactinomas can grow due to estrogenic stimulation. The risk of significant growth depends on the size of the prolactinoma prior to pregnancy. With microadenomas (<10 mm), the risk is considered to be low, whereas the risk is higher with macroprolactinomas (≥10 mm). Significant expansion may cause vision loss by compressing the optic chiasm. It is therefore appropriate to obtain visual field testing during pregnancy in women with macroadenomas even without symptoms to diagnose vision field loss (such as bitemporal hemianopsia) that may be due to an enlarging prolactinoma. Testing in these women is recommended every trimester of pregnancy. Because this patient is in her first trimester and has a history of a macroadenoma, visual field testing now is indicated.

It is not helpful to check the serum prolactin level. Prolactin is normally elevated in pregnancy and can be greater than 200 ng/mL (200 µg/L). Additionally, this patient has a known prolactinoma, so her prolactin will likely be elevated for both reasons. Elevated prolactin itself is not necessarily harmful. Prolactinomas cause concern when they cause hypogonadism or mass effect. In this patient, an elevated prolactin level will not change the treatment plan because it is expected to be elevated and does not help clarify whether the prolactinoma is causing harm.

Routine monitoring of women with prolactinomas with MRI during pregnancy is not indicated because the absolute risk of significant enlargement of pituitary adenomas is low. However, MRI is indicated in women with a pituitary macroadenoma and abnormalities on visual field testing or change in headache possibly attributable to expansion of the adenoma.

Bromocriptine is avoided in pregnancy when possible because its safety during gestation has not been established, although when a patient has symptoms of mass effect during pregnancy, bromocriptine may need to be restarted. However, it would not be appropriate to restart dopamine agonist therapy in this patient without a clear indication for treatment such as an enlarging pituitary adenoma.