Preterm labor remains to be one of the most important challenges of contemporary perinatology and constitutes the main reason of perinatal mortality and prematurity of neonates. Studies on preterm labor have confirmed the mutual interactions of several different hormonal systems while the activation of hypothalamic- pituitary- adrenal axis seems to have the greatest influence. It has been also suggested that size and mass of fetal adrenal glands may be associated with the risk of preterm labor. Several authors have shown that the evaluation of fetal adrenal gland volume may be a useful marker of fetal growth during pregnancy. Technological advancements enabled the development of three-dimensional ultrasound evaluation (3D) of the fetal adrenal glands, facilitating a more precise evaluation of their volume. Also, it seems to have higher sensitivity and specificity than two-dimensional ultrasonography (2D). Studies have confirmed a direct relationship between fetal adrenal gland size and the onset of preterm labor within at least 1 week since the ultrasound exam. They have also suggested that in a physiological pregnancy the relation between fetal zone and the whole organ remains constant throughout the pregnancy. Disruption of these proportions and fetal zone enlargement are considered to be a marker of labor cascade and preterm labor, with significantly higher sensitivity and specificity than ultrasound evaluation of the cervical length and assessment of the fetal fibronectin concentration.