Introduction. Subclinical hypothyroidism during pregnancy can be associated with numerous adverse outcomes. The purpose of this study was to compare short-term adverse pregnancy outcomes in treated versus nontreated patients who fall within the numerical range of thyroid-stimulating hormone (TSH) between the Iranian and American reference ranges. Materials and Methods. Eighty pregnant women with a known level of antithyroid peroxidase (anti-TPO) and TSH levels of 2.5–3.9 mIu/L in the first trimester and 3–4.1 mIu/L in the second and third trimesters were enrolled in the study and randomly assigned into two groups including 41 patients in the intervention group and 39 in the control group. The intervention group was treated with levothyroxine at least 50 μg/day and the control group received no treatment. The data were analyzed by SPSS software version 23. Results. The only significant findings were a correlation between pregnancy loss frequency (p − 0.011) and/or increased TSH level in the follow-up period (p = 0.008) with anti-TPO antibody positivity. Forty-four percent of mothers with positive anti-TPO Ab needed treatment initiation with levothyroxine, based on Iranian guidelines, due to increased TSH level during the follow-up period. Conclusion. Untreated pregnant women with subclinical hypothyroidism, who were placed in the intermediate range of TSH, recommended by Iranian and American guidelines, did not show any significant difference in short-term adverse pregnancy outcomes compared to the treated patients. Positive anti-TPO Ab may play a role in the development of short-term complications in mothers with subclinical hypothyroidism or it may increase the likelihood of an increase in TSH level during pregnancy.