Thyroid hormones play a crucial role in fetal growth and neurocognitive development. Our aim was to compare a weight-based dosing method of starting thyroxine to a fixed-dose method in newly diagnosed women with subclinical hypothyroidism during pregnancy.We performed a retrospective cohort study of consecutive women with newly diagnosed subclinical hypothyroidism during pregnancy seen at Mount Sinai Hospital and Womens' College Hospital, Toronto, Canada2015-2018.We identified women that were treated based on pre-pregnancy weightand those that were given a fixed dose of 50 mcg/day.The percent of women who reached the target TSH of <2.5 mIU/L within 4-8 weekswas compared using a Chi squared testand a logistic regression model, adjusting for age, initial TSH, and gestational age treatment was started.393 women were included: 252 treated using a fixed-dose approach; 141 treated based on pre-pregnancy weight. In the unadjusted analysis there was no difference between the groups in the percentage of women in the target range within 4-8 weeks (89.6% in the fixed-dose group vs 88.8% in the weight-based group (p=0.954). However, after adjustmentfor between-group differences in age, initial TSH, and gestational age treatment was started, there was a significantly greater odds of achieving the target range using the weight-based dosing (OR 4.26 (1.60-11.7), p=0.004).Treating women withnewly-diagnosedsubclinical hypothyroidism during pregnancy with a weight-based strategy increased the odds of reaching the target TSH range within 4-8 weeks. Clinicians caring for these women should consider this approach when starting treatment during pregnancy.
Balsam Bohlega, Afshan Zahedi, George Tomlinson, Denice S Feig