Aim: The aim of this study was to investigate the effect of first trimester thyroid-stimulating hormone (TSH) levels on fetal birth weight and maternal hemoglobin levels in pregnant women. Materials And Methods: Our study is a retrospective study of 293 singleton pregnant women admitted in the first trimester of pregnancy to the department of obstetrics and gynecology at second stage state hospital between March 2018 and April 2019. Those receiving treatment for thyroid diseases before pregnancy, those with diabetes mellitus, those who developed preeclampsia, patients with heart disease, smokers and alcohol users, and who delivered before 37 weeks were excluded from the study. The patients were divided into three groups according to TSH levels. The first group had TSH level <0.1 mU/L, the second group had TSH level 0.1-2.5 mU/L, and the third group had TSH level >2.5 mU/L. Groups were compared in terms of birth weight, delivery type and maternal hemoglobin value. Patients were divided into 3 groups according to their birth weights. These were groups of birth weights under 2500 grams, between 2500- 4000 grams and over 4000 grams and baby birth weights were compared according to maternal TSH levels. Results: There was no statistically significant difference between groups in terms of delivery type (p>0.05). Maternal first trimester hemoglobin levels were found to be significantly higher in patients with TSH levels less than 2.5 mU/L (p=0.001). Results were similar in terms of birth weights in all three TSH groups and no statistically significant difference was observed (p>0.05). Conclusion: Thyroid dysfunction is known to have a negative effect on the course of pregnancy. Further studies are needed to define the relationship between first trimester TSH level and fetal birth weight and maternal hemoglobin level.