Pituitary gland growth during normal pregnancy: an in vivo study using magnetic resonance imaging.

PURPOSE: Autopsy studies have shown that pregnancy results in physiologic pituitary enlargement. We used magnetic resonance imaging (MRI) to corroborate those findings in vivo.

PATIENTS AND METHODS: Based on gestational age, 32 normal primigravid patients were divided into three groups: Group I (n = 10), less than 12 gestational weeks; Group II (n = 11), 13 to 26 gestational weeks; and Group III (n = 11), 27 gestational weeks or more. The pituitary dimensions and volumes in these groups were compared with those in 20 healthy nulliparous women (control group).

RESULTS: MRI measurements showed a significant increase in pituitary volume in Groups I, II, and III when compared with the control group (p less than 0.001). Furthermore, there was an increase in pituitary volume between Groups I and II and between Groups II and III, although the former was not statistically significant (p greater than 0.05). At the end of pregnancy, the hypophysis had increased 2.6 mm in vertical, anteroposterior, and transversal dimensions, with an overall increase of 136 percent when compared with that of the control group.

CONCLUSION: Baseline measurements of the normal enlargement of the pituitary gland that occurs during pregnancy could prove useful when evaluating pregnant patients with suspected pituitary tumors or lymphocytic hypophysitis.