The most prevalent pathologies during pregnancy, such as hypertension, gestational diabetes mellitus (GDM), and intrauterine growth restriction (IUGR), can determine modifications in macro- and microscopic morphological features of the placenta and its free chorionic villi. In the fetus it may be accompanied by pathological manifestations, with the embryo’s future quality of life, and even its viability, at risk. The aim of this work is to perform a review of the morphological alterations that the placenta exhibits in pregnancies with GDM. A search on the topic in the scientific literature and specialized textbooks was carried out. The terms “placenta”, “diabetes mellitus gestational” and “gestational diabetes mellitus” were used to define the search. Among the morphological modifications it was found that the placental weight/fetal weight ratio is higher in GDM and is associated mainly with histological changes. The distance between maternal and fetal circulation is increased because of an increase in the chorionic villi on the surface as well as greater thickness of the syncytiotrophoblast basal membrane due to an increased type IV collagen deposition. The stroma between the villi is edematous, which modifies the metabolic and endocrinal function of these placentas. Moreover, the capillary surface is enlarged due to the phenomena of vascular neoformation and a greater penetration of these vessels within the villi. Low oxygen partial pressure (pO ) was detected, which would produce a compensatory hyperplasia of terminal chorionic villi. In GDM the placenta undergoes alterations in its formation, structure, and function. According to the review, these alterations are related to an oxygenation deficiency in the fetus and changes in the transplacental transport of nutrients and other alterations, causing fetal overgrowth by increasing their availability in addition to other consequences to the developing fetus. In the case of high blood pressure during pregnancy, this produces accelerated maturation and rapid aging of the chorionic villi, with the risk of inducing a placental abruption. In addition, placental circulation is reduced by a third, decreasing oxygen saturation in the umbilical vessels and placing the health of the fetus at risk.

KEY WORDS: Free chorionic villi; Gestational diabetes mellitus; Hypertension; Morphology; Placenta.