The VitDTracking study focuses on the relevance of maternal vitamin D levels and their association with prematurity, aiming to improve maternal and child health outcomes, particularly by reducing avoidable preterm births. In Portugal, vitamin D levels during pregnancy have never been studied. Epidemiological data from other countries reveal a high prevalence of vitamin D deficiency/insufficiency, especially in pregnant women. The hypovitaminoses prevalence remains high even with a supplementation dosage of 400 to 600 IU/day during pregnancy (dosage used in Portugal), which is considered as a suboptimal dose. This phenomenon is associated with adverse maternal and child outcomes, such as intrauterine growth restriction, preeclampsia, cholestasis, hypertension, and gestational diabetes as major causes of prematurity. Additionally, the Portuguese population has a higher prevalence of genome alterations that confer a lower capacity to produce vitamin D from sunlight exposure. These genetic characteristics are present in about 19% of the population, representing a prevalence four times higher than the European average (19% versus 4.75%), leading to a higher predisposition to vitamin D deficiency.