Chapter 49 Metabolic and endocrine disorders
At the end of this chapter, you will have:
Newborn metabolism
The transition from intrauterine to extrauterine life is a complex physiological process and includes many alterations in metabolic processes. Metabolic transition to extrauterine life is characterized by a shift from anabolic to catabolic metabolism. During pregnancy, anabolic metabolism synthesizes complex molecules from simpler ones to enable storage of energy, whereas catabolic metabolism breaks down complex molecules into simpler ones for the release of energy. This is a significant shift requiring the newborn infant to begin independent provision of energy for maintenance and growth (Blackburn 2007).
During the first week of life, there is a physiological weight loss and the normal infant can lose up to 10% of its birthweight; this can lead to an electrolyte imbalance causing transient metabolic disturbances which may or may not require treatment and vigilant observation is required by the midwife. For physiology, assessment and midwifery care of the newborn see Chapter 41. For more information on metabolic and endocrine disorders see website.
Acquired metabolic disorders
The majority of cases of hypoglycaemia are transient, occurring prior to the onset of regular feeding. Healthy term infants may have low glucose levels of 1–1.5 mmol/L but they cope with this by using alternative fuels, such as ketone bodies, lactate or fatty acids (Newell & Darling 2008).
Breastfeeding infants are particularly likely to have low blood sugar levels before feeding becomes established, but they have higher ketone body concentrations to use as an alternative metabolic fuel and therefore are unlikely to suffer any ill effects (Hawdon et al 1992, Newell & Darling 2008). An awareness of physiological hypoglycaemia is essential to ensure that infants are not unnecessarily investigated or treated unless there are other clinical indications for intervention.
Hypoglycaemia
There has been much debate over what constitutes a normal plasma glucose value for infants of different gestation and birthweight and, therefore, what constitutes a finite biochemical definition of hypoglycaemia (Cornblath et al 2000). A generally accepted definition of hypoglycaemia since the late 1980s that continues to be used in clinical practice is a blood glucose level of <2.6 mmol/L (Koh et al 1988).
Non-specific signs of hypoglycaemia in the newborn can be vague; they include lethargy, poor feeding and a degree of jitteriness. These signs can also be due to sepsis and sometimes a healthy term infant can be sleepy and reluctant to feed. If these non-specific signs persist or worsen, the midwife should seek immediate paediatric advice and anticipate investigations for sepsis and hypoglycaemia. Specific signs of hypoglycaemia comprise increasing lethargy and irritability with a reduction in level of consciousness and eventually seizures, which are associated with the risk of cerebral damage (Newell & Darling 2008).
Hypocalcaemia
Hypocalcaemia is most likely to arise in preterm infants, infants of diabetic mothers and following birth asphyxia. It can also be caused by renal failure and hypoparathyroidism. It may cause apnoea, jitteriness or seizures. Seizures due to hypocalcaemia, unlike those due to hypoglycaemia, have a good prognosis because they are not associated with long-term brain damage (Newell & Darling 2008). Severe symptoms will be treated with intravenous calcium. Long-term treatment will depend upon the cause.
