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Dysmorphic features may point to an underlying endocrine abnormality.
Approach to the problem
Midline defects, e.g. central cleft palate and/or lip, hypotelorism or hypertelorism.
Features of recognizable syndrome, e.g. Beckwith–Wiedemann syndrome (macroglossia, ear lobe creases, exomphalos), Smith–Lemli–Opitz (microcephaly, second- and third-toe syndactyly, see below), Robinow syndrome.
Other physical features to look for
Symmetrical growth retardation.
Micropenis (hypopituitarism, dysmorphic syndrome, see below).
In the neonate dynamic testing should not be undertaken without suitable indwelling lines, and under the advice of a paediatric endocrinologist. For pituitary function testing, or corticotrophin-releasing hormone (CRH) test, this means an arterial line for sampling. A short Synacthen test can usually be performed without an arterial line.
Anterior pituitary function tests
Measurement of random free thyroxine (fT4) and thyroid-stimulating hormone (TSH, after the initial postnatal surge in the first 2 days of life) provides information about pituitary and thyroid function.
Baseline gonadotrophin levels (leuteinizing hormone, LH; follicle stimulation hormone, FSH) can also be informative, as they should be relatively high in the newborn period.
Measurement of cortisol and growth hormone (GH) at the time of hypoglycaemia can be helpful, but, unlike older infants and children, the normal neonate may produce a good GH response to hypoglycaemia, but a poor cortisol response.
Measurement of several (at least 3) random cortisol levels is useful, as cortisol is released in a pulsatile manner and may be low (e.g. 50 nmol/L) in normal infants if measured at the nadir. Timing is not important as diurnal variation does not appear for 8–12 weeks. All samples could be on the same day (and therefore the results could be reported together).
Hypoglycaemia may be picked up incidentally in an asymptomatic baby.
Blood glucose should be measured regularly in vulnerable babies (see below).
Symptoms are non-specific:
Neuroglycopaenic symptoms of hypoglycaemia include apnoea, hypotonia, jittering, irritability, lethargy, abnormal cry, feeding problems, convulsions, and coma.
Autonomic symptoms (pallor, sweating, tachypnoea) are generally not prominent in the newborn.
Macrosomia may be present in infants of diabetic mothers.
Macrosomia in the absence of a history of maternal diabetes suggests hyperinsulinism.
Macrosomia with magroglossia, organomegaly, exomphalos, or ear lobe creases suggests Beckwith–Wiedemann syndrome (approximately 80% demonstrate genotypic abnormalities of the distal region of chromosome 11p).
Midline defects, micropenis, and jaundice suggest hypopituitarism (see Chapter 7).
Babies can have low blood glucose levels and be completely asymptomatic.
Approach to the problem
Asymptomatic healthy term babies of normal birth weight (9th to 91st centiles) do not require blood sugar measurements.
Symptomatic hypoglycaemia in a term baby is always pathological until proved otherwise.
Babies at risk of hypoglycaemia
Preterm or intrauterine growth retardation: lack of glycogen stores, immature enzymes involved in glucose homoeostasis, inappropriately high insulin levels.
History of birth depression: lack of glycogen stores due to utilization.
Infants of diabetic mothers, large-for-dates babies, babies with Beckwith–Wiedemann syndrome, babies with rhesus disease: excessive insulin secretion.
Polycythaemia: excessive metabolism of glucose by erythrocytes.
Autoimmune thyroid disease in the mother may influence fetal thyroid function by transplacental passage of thyroid receptor immunoglobulins which may either block or stimulate the fetal thyroid-stimulating hormone (TSH) receptor. In addition, thionamides used in the treatment of thyrotoxicosis in the mother may cross the placenta and render the fetus hypothyroid.
This is usually secondary to Hashimoto's thyroiditis and the mother may be producing thyroid inhibiting or rarely thyroid stimulating antibodies so the baby may develop transient hypo or very rarely hyperthyroidism.
If the maternal TSH receptor antibody titre is known, the risk to the baby can be assessed. TSH receptor antibody titres do not differentiate stimulating from blocking antibodies and both may co-exist (high titres will increase risk of hypo or hyperthyroidism). The TRH receptor antibody results differ depending on laboratory methods, and so normal levels will need to be assessed with reference to the laboratory norms.
If maternal TSH receptor antibody titre is normal, a Guthrie card TSH will suffice.
If the TSH receptor antibody titre is elevated or unknown, review the baby at 10 days to 2 weeks and measure TSH and fT4.
As risk of postnatal hypo or hyperthyroidism in baby is small, some would advocate no investigations are required.
Hypoglycaemia in infants of diabetic mothers should be anticipated and all infants should have early and regular glucose measurements until these are stable.
Hypoglycaemia may be asymptomatic or symptomatic.
Approach to the problem
Expectant management in all infants of diabetic mothers.
Early enteral feeds.
Regular (1–2 hourly) blood sugar measurements for first 12 h.
Other causes of hypoglycaemia (see Chapter 2).
Blood glucose level.
Other investigations for hypoglycaemia are not usually required unless hypoglycaemia is persistent.
Calcium and magnesium levels are required in symptomatic babies as symptoms overlap.
Haematocrit should be assessed if the baby appears plethoric or blood sugar is difficult to control (dilutional exchange transfusion may be required if the baby is polycythaemic).
If able to tolerate enteral feeds, increase the volume and frequency of the feeds.
If unable to tolerate feeds, commence an intravenous (IV) infusion and titrate the quantity of glucose to maintain the blood glucose concentration >2.6 mmol/L. Use a higher concentration of glucose via a central line (silastic long-line or umbilical venous catheter) rather than excess volumes of 10% dextrose as the latter is likely to result in fluid overload and hyponatraemia.
If IV access is difficult, intramuscular glucagon (100–200 µg/kg/dose) or buccal hypostop (40% glucose polymer, 1 mL/kg) may restore euglycaemia and buy time to achieve vascular access.
Immaturity (extreme preterm infant usually from the end of first week of life).
Congenital adrenal hyperplasia (usually days 4–10).
Congenital adrenal hypoplasia.
Renal impairment, e.g. polyuric phase of acute tubular necrosis (ATN), congenital nephrotic syndrome, Bartter syndrome (hyperprostaglandin E syndrome, associated with life-threatening hypokalaemia). Congenital renal abnormality (there may be a history of polyhydramnios secondary to excessive urine output in utero).