**5. A metabolic perspective**

When newborn transits to a life outside a womb, it must adapt to many new circumstances. One is metabolic transition, which is not as dramatic as, for example, changes in cardiopulmonary systems, but equally complex and essential for survival. As Colson [35] notices cardiopulmonary, immune and thermal adaptations are well documented, but most texts fail to describe the normal physiological metabolic transition from fetus to neonate.

Just after birth, as soon as the umbilical cord ceases to pulsate, placental circulation stops. This means that the constant supply of maternal nutrition especially glucose transferred via the placenta stops. Before the birth, no significant production of glucose has been demonstrated [36]. In utero insulin is being used as a growth hormone instead of being a metabolic regulator. Colson [35] explains that the processes of lipogenesis (formation and storage of fat in the form of adipose tissue) and glycogenesis (formation and storage of glucose in the form of glycogen in the liver, cardiac muscle and brain) are replaced by the metabolic pathways of neonatal life. These are glycogenolysis (breakdown of glycogen), lipolysis (breakdown of fats), gluconeogenesis (endogenous glucose production) and ketogenesis (formation of ketone bodies).These pathways imply a metabolic switch at birth from glucose to fat and therefore a diet initially lower in carbohydrate and high in fats. It is true that while neonatal blood glucose levels immediately fall in almost all healthy infants, it must adapt to intermittent feeding, digestion and intestinal absorption of nutrients (adapted from Colson, p. 13). The fetus prepares for his transition mainly by storing glycogen, producing catecholamines and depositing brown and white fat [37]. After the birth, hepatic glycogen stores are mobilized and hepatic synthesis of glucose from noncarbohydrate substrates enuses. This substrate enters the citric acid cycle and produces adenosine triphosphate, which serves as the energy source for the brain [37]. These events actually allow baby to gradually mobilize glucose to meet energy requirements. So-called transient neonatal hypoglycemia is a process of normal adaptation to extrauterine life, and it is important that we realize that in first 3–4 h healthy newborn could have low blood glucose levels.

Colson [35] exposes several practices that stand behind understanding of the normal metabolic physiology:


In order to optimize metabolic adaptation, babies and mothers must be kept closely together after birth. Health workers must encourage mothers to maintain close body contact with their babies as often as they want in an undisturbed environment [38].
