Few studies have explored the link between paraben exposure and thyroid hormone homeostasis in pregnant women across trimesters. The present study involved 97 pregnant women from southern Taiwan (2013-2014), and involved measuring urinary methyl, ethyl, propyl, and butyl parabens, as well as serum thyroid hormones and related indices, such as Structure Parameter Inference Approach-Glandular Disturbance [SPINA-GD], and SPINA Global Turnover [SPINA-GT]). Generalized estimating equations (GEE) were applied to examine the effect of longitudinal paraben exposure on thyroid hormone homeostasis. We found that propylparaben and butylparaben levels were associated with increased FT