Hemodynamic aspects of normal human feto-placental (umbilical) circulation

Understanding the changes in normal circulatory dynamics that occur during the course of pregnancy is essential for improving our knowledge of pathophysiological mechanisms associated with feto-placental diseases. The umbilical circulation is the lifeline of the fetus, and it is accessible for noninvasive assessment. However, not all hemodynamic parameters can be reliably measured in utero using currently available technology. Experimental animal studies have been crucial in validating major concepts related to feto-placental circulatory physiology, but caution is required in directly translating the findings of such studies into humans due to species differences. Furthermore, it is important to establish normal reference ranges and take into account gestational age associated changes while interpreting the results of clinical investigation. Therefore, it is necessary to critically evaluate, synthesize and summarize the knowledge available from the studies performed on human pregnancies to be able to appropriately apply them in clinical practice. This narrative review is an attempt to present contemporary concepts on hemodynamics of feto-placental circulation based on human studies.