© 2020 Informa UK Limited, trading as Taylor & Francis Group.Aims: To investigate if the maternal neck (NC) and waist (WC) circumferences measured in the first trimester of pregnancy have a predictive value in diagnosing gestational diabetes mellitus (GDM). Materials and methods: In this prospective study NC and WC of pregnant women were measured at 11–14th weeks. GDM was evaluated with a two-step oral glucose tolerance test at 24–28th weeks. Result: A total of 525 women were recruited; 49(9%) developed GDM. NC was positively correlated with WC (r: 0.583, p <.001), BMI (r: 0.533, p <.001), age (r: 0.123, p =.002), parity (r: 0.170, p <.001), and 50 g OGTT levels (r: 0.206, p <.001). Regarding the area under receiver operating characteristic (ROC) curve (AUC) analysis of NC and WC for predicting GDM were 0.585 (95% confidence interval (CI): 0.50–0.66, p =.043), and 0.693 (95%CI: 0.61–0.76, p <.001). The optimal cut off level of maternal NC was >38.5 cm, with 69% sensitivity and 45% specificity, and WC was >84.50 cm with a sensitivity of 78% and a specificity of 54%. Increased WC >84.50 cm (OR: 3.58, 95% CI:1.77–7.27; p <.001) and age >25 (OR: 3.05, 95% CI:1.38–6.72; p =.006) were independent predictors for the development of GDM adjusted for age, gravidity, parity, BMI, and NC. Conclusion: Maternal NC and WC were significantly higher in women with GDM; however, only maternal WC was a significant predictive marker for GDM in low-risk pregnant women.