There is a great deal of research interest regarding the underlying causes of slightly elevated TSH values in patients with subclinical hypothyroidism (SH) without abnormal findings on ultrasonography or anti-thyroid antibodies. Twelve infertile women with thyroglobulin antibody (TGAb) and thyroid peroxidase antibody (TPOAb)-negative nongoitrous SH were referred to our department of endocrinology between September 2007 and September 2015. None had been diagnosed with autoimmune thyroid disease or had any possible causes of SH. In all cases, LT4 was prescribed to bring TSH value below 2.5 mIU/L. Among those with infertility treatments, six (50%) became pregnant and gave birth to infants. Here, we report three of these six women who successfully became pregnant with infertility treatments and were found to have thyroid autoimmunity on data obtained during the postpartum period. Two developed postpartum thyroiditis, and the remaining one woman was temporarily weakly positive for TPOAb at 9 months postpartum. We describe three infertile subclinically hypothyroid women without goiter or anti-thyroid antibodies with potential thyroid autoimmunity. Thyroid autoimmunity is one of the most important issues for management of pregnant women, and thus, our findings are noteworthy for the care of infertile women with SH. This report provides valuable insights into the presence of autoimmunity in nongoitrous thyroid-associated antibody-negative SH patients.