The aim of this study is to explore the relationship between high cord blood thyroid-stimulating hormone (TSH) level and in-utero stress to the fetus in gestational diabetes mellitus (GDM). Cord blood TSH results were analyzed in 1,578 euthyroid infants from singleton pregnancies with GDM: 103 with elevated TSH (>16 mIU/l) and 1,475 with normal TSH. Maternal characteristics, pregnancy outcome and perinatal complications were compared between the two groups. Multiple logistic regression was used to study the association between high cord blood TSH level and various perinatal complications which reflect in-utero stress in GDM after adjusting for the confounding effects of parity, instrumental delivery, cesarean section and baby gender. High cord blood TSH level was found to be associated with the 1-min Apgar score <7 (OR 3.31, 95% CI 1.78-6.16), birth trauma (OR 3.44, 95% CI 1.11-10.69), neonatal jaundice requiring treatment (OR 2.08, 95% CI 1.30-3.32), neonatal sepsis (OR 2.34, 95% CI 1.24-4.42), respiratory complications (OR 3.45, 95% CI 1.37-8.70), neurological complications (OR 8.01, 95% CI 1.91-33.60) and overall perinatal morbidity (OR 2.41, 95% CI 1.58-3.67). Cord blood TSH level seems to be a better and independent indicator of the in-utero stress to the fetus in GDM when compared to the commonly used sugar profile result and HbA1c level.