Temporal trends in thyroid-stimulating hormone and live birth rate in subclinical hypothyroid patients in a recurrent pregnancy loss population

Objectives: The purpose of this study was to explore if thyroperoxidase antibody positivity impacts thyroid stimulating hormone levels during pregnancies following the index visit and how live birth rate is impacted when treated subclinical hypothyroidism is treated with levothyroxine or not. Study design: A retrospective chart review of 1443 recurrent pregnancy loss patients from BC Women's Hospital recurrent pregnancy loss clinic was conducted. Thyroid stimulating hormone in pregnancies after the index visit across thyroperoxidase antibody status was analyzed using mixed-effects linear regression. Live birth rate in patients with subclinical hypothyroidism (thyroid stimulating hormone 2.5–10 mIU/L) with levothyroxine treatment was compared to those without relative to euthyroid patients using logistic regression. Results and conclusions: There was no significant difference in patient demographics including age, body mass index, or number of previous live births or pregnancy losses between groups. The distribution of recurrent pregnancy loss causes between groups revealed no difference in proportion of patients with anti-phospholipid antibody syndrome, hereditary thrombophilia, hyperprolactinemia, or anatomic causes. There was no significant change in thyroid stimulating hormone across thyroperoxidase antibody or treatment status (p = 0.24) for up to four subsequent pregnancies. An increased live birth rate in subclinical hypothyroidism when treated with levothyroxine relative to untreated (OR = 2.25, p < 0.001) was seen. Thyroid stimulating hormone values do not change over time following the index visit for up to 4 subsequent pregnancies irrespective of the thyroxperoxidase antibody status. An increase in live birth rate was found in patients with borderline subclinical hypothyroidism when treated with levothyroxine.