Background: Thick Nuchal Translucency detection by ultrasound has emerged as a powerful prenatal screening strategy to diagnose a myriad of birth defects and syndromes. Abnormal Nuchal Translucency thicknesses should be correlated with further non-invasive or invasive maternal tests either to reassure parents or manage the abnormality with confidence. Upon thorough literature review there is no data regarding the reference range and prevalence of abnormal nuchal translucency and its association with birth defects in Ethiopia despite that Nuchal Translucency measurement is easy to perform, non-invasive and powerful screening tool. There exists significant variation of nuchal translucency thickness with maternal age and gestational age. Objective: Determining the reference range of fetal nuchal translucency thickness and associated factors that affect nuchal translucency value in pregnant women in their 11th to 13+6th weeks of gestation in women having ANC follow up in Bahir Dar City , Northwest Ethiopia. Methods: An institutional based cross-sectional study was conducted from September, 2021to December, 2021 among pregnant women within gestational period of 11th -13+6th week. The necessary data was collected after structured questioner is prepared. Using transabdominal scanning, fetal nuchal translucency thickness and crown ramp length were measured using ≥3.5 MHz curvilinear probe. The data was collected in Bahirdar by trained senior radiology residents, radiologists and obstetricians from September, 2021 to December, 2021. Data was entered using Epi Data software and analyzed using SPSS software version 23. Various descriptive statistics such as frequencies and proportions were computed to describe the outcome variable. Then resulted were presented using tables, figures and text narration. The association between the outcome and independent variables were assessed using multivariable logistic regression analysis. The strength of association was described using odds ratio at 95% CI and statistical significance determined by a p-value less than 0.05. Results: The mean age of the study participants was 26.4 years (range 16-45). The mean nuchal translucency thickness was 1.88 mm and ranges from 0.5 mm to 6.7 mm with 96.3% of the study participants having values less than 3.0 mm. 1.2 % of the study participants had NT thickness of 3.0-3.4 mm and 2.5 mm had NT thickness of ≥ 3.5 mm. The thickness of nuchal translucency had significant association with parity and gestational age. Conclusions: The overall mean nuchal translucency thickness was 1.88 mm and its upper limit was 6.7 mm. 3.7 % of the participants had NT thickness value of ≥ 3.0 mm. The nuchal translucency had significant association with parity and gestational age. Key Words: Nuchal translucency, Parity, Gestational age, Crown Rump Length