Serum pituitary antibodies in normal pregnancy and in patients with postpartum thyroiditis: a nested case-control study.

Objectives: The aim of this study was to evaluate antipituitary antibody (APA) prevalence in a series of patients with postpartum thyroiditis (PPT) during pregnancy and in the postpartum.

Design: We conducted a nested case-control study on consecutive PPT and normal pregnant women at the Centre for Endocrine and Diabetes Sciences in Cardiff and at the Department of Endocrinology in Pisa.

Methods: We enrolled 30 women with PPT: 17 were hypothyroid (Hypo), 7 with hyperthyroidism (Hyper) and 6 with a transient hyperthyroidism followed by hypothyroidism (Biphasic). Twenty-one healthy pregnant women served as controls. APA (measured using indirect immunofluorescence), free thyroxine, free triiodothyronine, TSH, antithyroid autoantibodies, and thyroid ultrasound were performed during pregnancy and postpartum. The stored sera have been sent to Pisa, where serum APA, IGF1, and cortisol were measured.

Results: APA were found in 8 out of the 30 PPT patients (26.7%) and in one normal pregnancy (4.7%, P=0.063). Three out of the seventeen Hypo with PPT (17.6%), three out of the seven Hyper PPT (42.8%), and two out of the six Biphasic PPT (33.3%) were positive for APA. APA prevalence was not significantly different in the PPT subgroups (P=0.453). With one exception, APA all increased in the postpartum period (87.5%, P<0.016). Basal serum IGF1 and cortisol were in the normal range with the exception of two patients with positive APA who presented low serum IGF1 levels (36 and 45 ng/ml).

Conclusions: APA are frequently present in the postpartum period in patients affected by PPT. Further studies are necessary to evaluate whether APA in PPT patients are associated with pituitary function impairment.