This review critically evaluates the biopsy techniques used to assess placental bed vascular pathology and summarizes the key features of defective deep placentation, which is associated with a spectrum of obstetrical syndromes including preeclampsia, intrauterine growth restriction (IUGR), preterm labor, preterm premature rupture of membranes (PROM), abruptio placentae, and spontaneous midtrimester abortion. The review proposes a classification of defective deep placentation into three types based on the degree of restriction of remodeling and the presence of obstructive lesions in the myometrial segment of the spiral arteries. The study highlights the importance of understanding the mechanisms underlying defective deep placentation to improve the characterization and diagnosis of placental disorders, and to develop diagnostic and predictive markers for adverse pregnancy outcomes.This review critically evaluates the biopsy techniques used to assess placental bed vascular pathology and summarizes the key features of defective deep placentation, which is associated with a spectrum of obstetrical syndromes including preeclampsia, intrauterine growth restriction (IUGR), preterm labor, preterm premature rupture of membranes (PROM), abruptio placentae, and spontaneous midtrimester abortion. The review proposes a classification of defective deep placentation into three types based on the degree of restriction of remodeling and the presence of obstructive lesions in the myometrial segment of the spiral arteries. The study highlights the importance of understanding the mechanisms underlying defective deep placentation to improve the characterization and diagnosis of placental disorders, and to develop diagnostic and predictive markers for adverse pregnancy outcomes.