**Abstract**

 A detailed discussion of normal placental development and physiology is beyond the scope of this chapter and is discussed in other chapters. Instead, this chapter will focus on an overview of congenital placental abnormalities and the obstetrical complications that can arise. The goal of this chapter is to delineate the real-world implications of placental abnormalities and provide the reader with a basis for understanding the other chapters that will delve into microbiology, genomics, immunohistochemistry, and biochemistry of the placenta. The focus of this chapter will be on the developmental anomalies and this chapter will not discuss acquired anomalies (e.g., chorioamnionitis, amnion nodosum, metastatic tumors, and umbilical cord true knots). As the intention of this chapter is to focus on the etiopathogenesis of abnormal placentation, it is not intended to instruct the medical management of the described conditions, and therefore the discussions of management will be brief. The information provided is intended for general knowledge only and is not intended for use in diagnosing or treating a health problem or disease without consultation with a qualified healthcare provider. This chapter is not a substitute for professional medical advice, or treatment for specific medical conditions.

**Keywords:** abnormal placentation, intrinsic placental abnormalities, implantation abnormalities, placental perfusion, placenta accreta, placenta previa, ectopic pregnancy, abruption, hematoma, vasa previa, circumvallate placenta, chorioangioma, amniotic band sequence, placenta membranacea, battledore placenta, single umbilical artery, velamentous umbilical cord, preterm labor, intrauterine growth retardation, intrauterine fetal demise, pregnancy complications, high-risk pregnancy, maternal-fetal medicine, embryology, fetal development, fetal intervention, obstetrical emergency, fetal surgery
