Update on the cardio-vascular adaptation at birth

Background Worldwide, millions of babies are born each day, and in many of these infants, the umbilical cord is severed and they must begin air-breathing to survive. These events dramatically change the infant’s circulation, transforming it from the fetal to the postnatal form, which then persists for the rest of its life[1,2]. However, if an infant is not breathing at birth, umbilical cord clamping will reduce venous return to the infant’s heart (preload) by ~50% and increase systemic vascular resistance (afterload); both of which decrease cardiac output[3]. Cardiac output will remain low until breathing commences, when it triggers the increase in pulmonary blood flow needed to restore preload for the heart[4]. We have recently discoveredthat commencing ventilation before the umbilical cord is clamped, which is arguably the most natural sequence of events, stabilizes the circulation and avoids the loss and then restoration in cardiac output after birth[5]. Further, we demonstrated that it improves systemic and cerebral oxygenation by preventing the infant from becoming hypoxic during the transition at birth [6]. Our current research aims to examine how the infant’s position, above or below the placenta, and uterine contractions induced by oxytocin administration, influences umbilical blood flow and the distribution of blood between infant and placenta during delayed umbilical cord clamping (DCC) at birth.