McCune-Albright syndrome: growth hormone dynamics in pregnancy

Excess GH secretion has a well recognized association with McCune-Albright syndrome. Although there have been a number of reported pregnancies in uncontrolled acromegaly, none has been described in the McCune-Albright syndrome. We have studied the GH and insulin-like growth factor I (IGF-I) profiles in a patient with confirmed McCune-Albright syndrome and GH hypersecretion throughout a successful pregnancy and postpartum period. Prepregnancy, IGF-I was 60.6 nmol/L (normal, 18.0--43.1), and the daytime GH profile measured using assay A was 9.6--14.0 mU/L. At 13 weeks gestation there was a decline of IGF-I to 33.9 nmol/L and in the daytime GH profile (assay A) to 5.4--6.8 mU/L. At 24 weeks, IGF-I had risen to 51.6 nmol/L. A simultaneous daytime GH profile at this time using assay A revealed levels between 21.3--22.1 mU/L, but only 2.1--3.0 mU/L with assay B. Assay A has significant cross-reactivity with human placental lactogen (HPL), unlike assay B. At 36 weeks, IGF-I was still elevated at 56.6 nmol/L, with a daytime GH profile of 16.6--17.7 mU/L using assay A and 1.5--3.9 mU/L with assay B. At 12 weeks postpartum, IGF-I was 71.4 nmol/L, and the daytime GH profile with assay B was 5.6--8.6 mU/L. These data support a picture of GH suppression during pregnancy in acromegaly associated with McCune-Albright syndrome, shown best with assay B, which discriminates between GH and HPL. These results contrast with previous reports of pregnancy in uncontrolled acromegalics, in whom pituitary GH levels were unaffected by pregnancy, and total GH and IGF-I levels were noted to be elevated. These data suggest that GH secretion in a pregnant acromegalic with the McCune-Albright syndrome may not be entirely autonomous, as seen in classic acromegaly, but may be associated with a degree of negative feedback control that could be exerted by a circulating factor of placental origin, probably HPL or placental GH.