Background: A good metabolic control in Gestational Diabetes Mellitus (GDM) is crucial to avoid complications in the mother and the offspring. A limitation to reach a desired HbA1c in GDM is the education level of the mothers. Aims: The aim of this study was to determine the correlation between the HbA1c and the points obtained in a basic mathematical test. Study Design: cross-sectional study. Methods: This was a pilot study, prospective and cross-sectional. Pregnant women, older than 18 years old, diagnosed with GDM were invited to participate resolving a mathematical test of ten questions. HbA1c was done in the first consultation. Spearman correlation test was used between HbA1c and the punctuation of the mathematical test. Results: 31 patients with a mean age of 29 ± 6.7 years old accepted to participate. The education level was as follows: 5 (16.12%) with Primary School, 20 (64.51%) with High School, 2 (6.45%) with Preparatory School, 2 (6.45%) with technical studies and 1 (3.22%) that finished the University. The Spearman test showed a negative correlation between the mathematical test and the HbA1c (r2 = -0.395, P ≤ 0.001). Conclusion: A low mathematics knowledge limits the expectation to get an optimal metabolic control in GDM.