Association between thyroid autoimmunity and the decline of ovarian reserve in euthyroid women

Research question Is thyroid autoimmunity (TAI) associated with the decline of ovarian reserve in euthyroid women? Design Case-control study. Data from 4302 euthyroid women with normal ovarian reserve (NOR) and low ovarian reserve (LOR), including biochemical premature ovarian insufficiency (POI) and overt POI, were retrospectively analysed. The prevalence and effect of TAI on ovarian reserve was evaluated between women with NOR and LOR. Status of ovarian insufficiency and TSH levels was further stratified for analysis. The correlation between anti-thyroid peroxidase antibody (TPOAb), anti-thyroglobulin antibody (TgAb) titres and ovarian reserve markers was also determined. Results The prevalence of positive TAI and TgAb was equally distributed between women with NOR and LOR (P = 0.080, P = 0.172); the prevalence of TPOAb positivity was higher in the LOR group (P = 0.005). After stratifying ovarian reserve and TSH, positive TAI, TPOAb and TGAb were significantly associated with overt POI when TSH was >2.5 µIU/ml (all P < 0.001); no association was observed with biochemical POI or overt POI when TSH was ≤2.5 µIU/ml. No correlation was found between TPOAb, TGAb titres and AMH (P = 0.218, P = 0.368, respectively), and bilateral AFC (P = 0.184, P = 0.315, respectively) in patients with LOR; only TPOAb titre was positively correlated with FSH (P = 0.039). Conclusions Among the whole population of euthyroid women, TAI was not associated with low ovarian reserve but was significantly associated with overt POI in women with TSH>2.5 µIU/ml. Further basic studies on underlying mechanisms are needed.