Background: Pregnancy causes mechanical, anatomic, and hormonal changes that impact sleep patterns and the pregnant woman's quality of life. Objectives: This study aimed to assess the sleep-related breathing disorders among pregnant women in the third trimester compared to non-pregnant women. Patients and Methods: The study was conducted in the Department of Obstetrics and Gynecology and the Department of Chest Diseases, Faculty of Medicine, Assiut University. A cross-sectional study was carried on 176 women, assigned into two groups, 88 women in their 3ed trimester of pregnancy and 88 non-pregnant women as a control group. All study participants had been evaluated as regards their sociodemographic characteristics, clinical data, maternal, neonatal outcome, STOP, STOP-Bang questionnaires and polysomnography parameters. Results: Regarding STOP and STOP-Bang questionnaires, the highest percentages were 60.2%, 50% in pregnant and non-pregnant women had snore loudly, respectively with no significant difference. There was significant difference between the two groups regarding feeling tired, BMI > 35 kg/m2, and having neck circumference > 40 cm. There was a significant difference between pregnant and non-pregnant women in term of total snoring score (total score ≥ 3 in 42% of pregnant group, and 12.5% in non-pregnant group). Conclusion: As joint difficulties in the third trimester of pregnancy, sleep disruption and its accompanying sleep disorders are mostly ignored. Sleep quality or sleep-related breathing difficulties are closely linked to pregnancy-related medical issues such as preeclampsia and gestational hypertension. Poor sleep quality in the third trimester was associated with advanced maternal age, advanced gestational age, and multiparity.