Objective: Subclinical hypothyroidism may cause complications during the pregnancy. The effect of subclinical hypothyroidism treatment during pregnancy is unknown. The main challenge is to determine an upper limit in which women might experience negative pregnancy outcomes. This study was conducted to assess the subclinical hypothyroidism treatment prognosis in pregnant women in an obstetrical tertiary referral center. Design: A retrospective case-control study Setting: This study was conducted from 2015 to 2019 in a tertiary obstetrical referral center in Iran, Tehran. Population: The patients who were referred to obstetrical clinics for prenatal care entered the study. Methods: A questionnaire was filled for each patient consisting of detailed information about the patients. The patients were followed up until labor and all pregnancy outcomes were noted. The results were compared using SPSS 24 and the P<0.05 was considered the significance level. Result: A total number of 155 patients with the mean age 28.74±5 was referred to the clinic. 80 patients were in the case group while in the control group there were 42 pregnant women. There was a statistical difference between patients positive for Anti-TPO and negative ones (P<0.05). Conclusion: Though there was a significant difference in the TSH level between the two groups, the pregnancy outcomes did not differ among patients. Although the necessity of treatment in this clinical condition is still controversial, it might reduce some neurological damages in neonates and pregnancy complications in mothers.