The "Great Obstetrical Syndromes" are associated with disorders of deep placentation, a condition involving abnormal vascular remodeling of the spiral arteries in the placental bed. This condition is linked to various pregnancy complications, including preeclampsia, intrauterine growth restriction (IUGR), preterm labor, preterm premature rupture of membranes (PROM), abruptio placentae, and spontaneous abortion. The study highlights the importance of understanding the physiological transformation of spiral arteries in the placental bed, which is crucial for diagnosing and managing these conditions. Defective deep placentation is characterized by impaired remodeling of the spiral arteries, leading to reduced blood flow to the placenta. This can result in inadequate oxygen and nutrient supply to the fetus, contributing to adverse pregnancy outcomes. The review discusses the classification of defective deep placentation into three types based on the degree of remodeling restriction and the presence of obstructive lesions in the spiral arteries. The process of spiral artery remodeling during pregnancy involves two waves of trophoblast invasion. The first wave occurs in the decidua, while the second wave involves the myometrial segment of the spiral arteries. Defective remodeling can lead to various obstetrical syndromes, including preeclampsia, IUGR, preterm labor, and abruptio placentae. The study emphasizes the importance of placental bed biopsies in assessing vascular pathology and understanding the underlying mechanisms of these conditions. The review also discusses the role of uterine artery Doppler velocimetry and other imaging techniques in evaluating placental vascular health. However, these methods have limitations in assessing the full extent of vascular remodeling. The authors propose a classification system for defective deep placentation that may improve the understanding of these conditions and their pathophysiology. In conclusion, disorders of deep placentation are a significant factor in various obstetrical syndromes, and understanding the mechanisms of spiral artery remodeling is essential for the diagnosis and management of these conditions. Further research is needed to develop more effective diagnostic and therapeutic strategies for these complications.The "Great Obstetrical Syndromes" are associated with disorders of deep placentation, a condition involving abnormal vascular remodeling of the spiral arteries in the placental bed. This condition is linked to various pregnancy complications, including preeclampsia, intrauterine growth restriction (IUGR), preterm labor, preterm premature rupture of membranes (PROM), abruptio placentae, and spontaneous abortion. The study highlights the importance of understanding the physiological transformation of spiral arteries in the placental bed, which is crucial for diagnosing and managing these conditions. Defective deep placentation is characterized by impaired remodeling of the spiral arteries, leading to reduced blood flow to the placenta. This can result in inadequate oxygen and nutrient supply to the fetus, contributing to adverse pregnancy outcomes. The review discusses the classification of defective deep placentation into three types based on the degree of remodeling restriction and the presence of obstructive lesions in the spiral arteries. The process of spiral artery remodeling during pregnancy involves two waves of trophoblast invasion. The first wave occurs in the decidua, while the second wave involves the myometrial segment of the spiral arteries. Defective remodeling can lead to various obstetrical syndromes, including preeclampsia, IUGR, preterm labor, and abruptio placentae. The study emphasizes the importance of placental bed biopsies in assessing vascular pathology and understanding the underlying mechanisms of these conditions. The review also discusses the role of uterine artery Doppler velocimetry and other imaging techniques in evaluating placental vascular health. However, these methods have limitations in assessing the full extent of vascular remodeling. The authors propose a classification system for defective deep placentation that may improve the understanding of these conditions and their pathophysiology. In conclusion, disorders of deep placentation are a significant factor in various obstetrical syndromes, and understanding the mechanisms of spiral artery remodeling is essential for the diagnosis and management of these conditions. Further research is needed to develop more effective diagnostic and therapeutic strategies for these complications.