Two maternal uterine arteries supply the placenta—oxygenated blood travels from the mother through the placenta; O₂ diffuses across the placenta, binds with neonatal hemoglobin, and is then carried by a single umbilical vein to the body of the fetus. Deoxygenated blood is returned from the fetus to the placenta by two umbilical arteries. As one would expect, at birth, umbilical arterial blood is lower in pH and O₂ and higher in CO₂ compared with umbilical venous blood (Table 198-1). Umbilical cord blood gas measurements can serve to assess the fetal condition immediately after delivery. Umbilical arterial measurements represent the fetal condition, whereas umbilical vein measurements would represent the maternal condition if the blood were withdrawn prior to cross-clamping the umbilical cord, as well as uterine placental gas exchange.

The majority of births do not require active intervention to establish adequate cardiorespiratory function in the newborn because most newborns undergo a relatively smooth physiologic transition at birth. However, it is of utmost importance to have skilled practitioners available at the time of birth to provide dedicated assessment and resuscitation of the newborn as needed. Such individuals should be capable of managing the airway and have a working knowledge of neonatal physiology and pathology, including vital sign parameters, laboratory values, common congenital anomalies, and their immediate implications. Adequate equipment and resources should be available and checked prior to delivery and should include, at the very minimum, airway supplies (e.g., appropriately sized laryngoscopes, tracheal tubes, and masks), a warming device, suction catheters connected to a suction system, O_2, and the ability to provide positive-pressure ventilation, in addition to emergency medications.