Prolactin-secreting adenomas account for approximately 30% of all pituitary adenomas. Fewer than 7% of patients with intrasellar microadenomas (size less than 10 mm) manifest clinical evidence of tumor expansion during pregnancy. On the other hand, macroadenomas (size greater than 10 mm) are associated with a 17% incidence of complications during pregnancy. Symptoms of headache, visual disturbance, and nausea are the most common. These symptoms tend to occur most frequently during the first trimester and can be mistaken for symptoms of pregnancy.

For patients with microadenomas treated with bromocriptine to achieve pregnancy, the drug should be discontinued as soon as pregnancy is diagnosed. It is generally accepted that periodic measurement of serum prolactin levels are of minimal benefit during pregnancy, since serum prolactin levels do not always rise with pregnancy-induced tumor enlargement. Because of the low incidence of microadenoma growth during pregnancy, it is not necessary to perform routine visual field testing. Routine clinical evaluation with particular attention to symptoms of headache and visual disturbances constitutes prudent follow-up. For patients with known microadenomas who become symptomatic, immediate computed tomography (CT) scanning or magnetic resonance imaging (MRI) is indicated.

For women with macroadenomas confined to the sella, the risk of enlargement during pregnancy is small. For women with larger macroadenomas that have suprasellar extension, there is a 15% to 35% risk of clinically significant tumor enlargement during pregnancy. Patients with suprasellar extension of their tumors should consider transsphenoidal tumor resection before conception. Unfortunately, tumor growth during gestation cannot be predicted by prepregnancy tumor size or serum prolactin concentration. Patients at highest risk include those with neurologic or visual symptoms before pregnancy.

All patients with macroadenomas should have monthly neurologic examinations and visual field tests. As with microadenomas, periodic serum prolactin levels are not helpful. CT scanning or MRI should be performed when tumor growth is clinically suspected. Bromocriptine can be used during pregnancy to decrease tumor size rapidly. In previously symptomatic patients with suprasellar extension, continuation of bromocriptine throughout pregnancy is prudent, since sudden reexpansion of the tumor has been reported. Surgery is rarely necessary.

There is no evidence that breast-feeding causes tumor enlargement. Nevertheless, patients with macroadenomas should be followed closely for symptoms or signs of tumor expansion during breast-feeding.