en Endocrinology Endocrinology Original Research Original Research <p> <strong> Background </strong>:Subclinical hypothyroidism may adversely affect In Vitro Fertilization (IVF) outcomes. However the cutoff of thyroid-stimulating hormone (TSH) for diagnosis and treatment is controversal. The aim of this study was to find the association of clinical pregnancy rate with regard to TSH levels in women undergoing IVF. </p><p> <strong> Methods: </strong>A historical cohort study of 816 infertile patients who underwent IVF in 2011 and 2012 was conducted. The study subjects were categorized in two groups according to their baseline TSH level one with 0.5 ≤TSH< 2.5 mIU/L and other with 2.5 ≤TSH< 4.5 mIU/L. All patients were followed up for 6 weeks after embroyonic transfer. The outcomes of the study were consisted of rates for Human Chorionic Gonadotropin (HCG) and evaluation of their clinical pregnancies. </p><p> <strong> Results: </strong>About 60% of the study subjects had serum TSH level < 2.5 mIU/L and 40% ≥ 2.5 mIU/L. There were no statistically significant differences in age, years of infertility, BMI, baseline FSH and estradiol level of patients and the type of induction protocols between the study groups. The HCG rise was occurred in 30.4% of the subjects with TSH level < 2.5 mIU/L versus 26.3% of the subjects with TSH ≥ 2.5 mIU/L (p value= 0.2). The clinical pregnancy rates in the group of patients with TSH < 2.5 mIU/L and those with ≥ 2.5 mIU/L were 27.1% and 23.9% respectively (p value= 0.3). <strong></strong></p><p> <strong> Conclusion: </strong>Our results were similar to various studies in which reported lack of association between TSH level in the range of 0.5- 4.5 mIU/L and IVF outcomes. It seems that lowering the upper limit of normal TSH should be still considered as a scientific debate. </p> Thyroid stimulating hormone, clinical pregnancy, In Vitro Fertilization. Subclinical hypothyroidism. 283 286 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1-676&slc_lang=en&sid=1 Marziyeh Aghahosseini ivfshariati69@gmail.com 200319475328460012833 200319475328460012833 No Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Homa Asgharifard asgharifard@razi.tums.ac.ir 200319475328460012834 200319475328460012834 Yes Former resident of Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Ashraf Aleyasin ivfshariati69@gmail.com 200319475328460012835 200319475328460012835 No Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran Arash Tehrani Banihashemi tehranib@gmail.com 200319475328460012836 200319475328460012836 No Department of Epidemiology, Iran University of Medical Sciences, Tehran, Iran.