Previous Live Births and Induced Abortions May Precede Later Development of Graves' Hyperthyroidism

To investigate the association between reproductive history and later development of various nosological subtypes of overt hyperthyroidism.

From the Danish population, we included incident hyperthyroid women, and for each case we recruited 4 euthyroid age-sex-region-matched controls from the same sub-population. Hyperthyroid cases/controls were: Graves' disease (GD, n = 232/928), multinodular toxic goitre (MNTG, n = 91/364), solitary toxic adenoma (STA, n = 21/84). Patients diagnosed with hyperthyroidism within 1 year after delivery including post-partum GD were excluded. In multivariate conditional regression models (reference: no reproductive events), we analysed the association between development of GD/MNTG/STA and reproductive factors such as age at menarche/menopause, reproductive span, number of pregnancies/childbirths/abortions, investigations for infertility, and years on oral contraceptives. We adjusted for possible confounders such as alcohol intake, smoking, co-morbidity, and education. Age was studied as a potential effect measure modifier.

GD patients diagnosed before the age of 40 years had given births more often than control subjects (OR [95% CI] for 1/2/3+ births [ref.: nulliparous] were 1.57 [0.80-3.11]/2.06 [1.001-4.22]/3.07 [1.50-6.26]), and they had induced abortions performed more often (OR for 1/2+ induced abortions [ref.: no: events] were 0.99 [0.54-1.84]/2.24 [1.12-4.45]). No associations were observed between any reproductive factor and the development of MNTG or STA.

Childbirths and induced abortions may be followed by development of Graves' hyperthyroidism after the post-partum period. This was not the case for the non-autoimmune subtypes of hyperthyroidism.