Du YJ, et al. - Researchers examined the effects of long-acting gonadotropin-releasing hormone agonist (GnRH-a) on thyroid function in euthyroid patients of in vitro fertilization (IVF)/ intracytoplasmic sperm injection of embryo transfer (ICSI-ET). Further, they investigated the timing and alteration of thyroid stimulating hormone (TSH) during controlled ovarian stimulation (COS). Two hundred seven euthyroid patients scheduled for IVF/ICSI were divided into two groups based on basal serum TSH level: group A with 0.35mIU/L＜TSH＜2.5mIU/L (n = 137) and group B with 2.5mIU/L ≤ TSH＜4.5mIU/L (n = 70). Long-acting GnRH-a injection led to a significant increase in serum TSH level in both groups, this may relate to the possible development of subclinical thyroid dysfunction. Findings suggest a higher susceptibility of infertile patients with serum TSH > 2.5mIU/L to GnRH-a while a higher clinical pregnancy rate was noted among patients with basal TSH less than 2.5mIU/L when receiving IVF/ICSI.