Studies evaluating pregnancy outcomes after assisted reproductive treatment (ART) in women with high-normal (2.5-4.5 mIU/L) thyroid-stimulating hormone (TSH) levels are conflicting, possibly due to different patient charactistics and subfertility indications. The aim of this study was to examine the hypothesis that high-normal compared to low-normal TSH levels are associated with adverse implications for pregnancy outcomes in conventional in vitro fertilization (IVF)treated women. Therefore, we analyzed retrospectively the characteristics and pregnancy outcomes of 949 subfertile women with TSH 0.3-4.5 mIU/L, treated with conventional IVF between January 2008 and March 2012. Demographic and baseline characteristics were compared between groups of patients based on TSH quartiles, using one-way Anova, Kruskal-Wallis ANOVA and chi-square test. Women with high-normal quartile TSH were significantly more likely to be primary subfertile (P = 0.01), with a higher prevalence of unexplained subfertility and with 15% fewer live births after IVF compared to lower TSH quartiles (P = 0.02). In secondary subfertile women with high-normal TSH, male factor subfertility prevailed (P = 0.01), with more live births (P = 0.01). When analyzing primary and secondary subfertile women as one group, these differences failed to be observed, showing no differences in cumulative pregnancy outcomes of IVF between TSH quartiles (I: 0.3-1.21 mIU/L; II: 1.22-1.68 mIU/L; III: 1.69-2.31 mIU/L; IV: 2.32-4.5 mIU/L). In conclusion, primary subfertile women predominate in the high-normal TSH quartile, associated with significantly fewer live births in a subgroup of primary unexplained subfertile women (9%; n = 87/949), while in secondary subfertile women, dominated by male factor subfertility, high-normal TSH is associated with more live births.