Neonates/newborns hypothyroidism

Hormone Neonates with hypothyroidism pefore therapy, 5-7 days of age) (n = 8) Healthy neonates (newborn 5-7 days of age) (n = 8) p value Neonates with hypothyroidism (after 8 weeks of therapy) (n = 8) Healthy neonates (after 8 weeks of therapy) (n = 8) p value... 

Serum TSH and thyroxine concentrations have been measured 57 days after birth in 365 healthy newborns whose umbilical stump had been treated with 10% povidone-iodine (41). The prevalence of high TSH concentrations was significantly higher in this group than in the general population (3.1% versus 0.4%), as was the rate of transient hypothyroidism (2.7% versus 0.25%). All the children were normal when retested 1 week later. Transient hypothyroidism due to skin contamination with povidone-iodine occurred in a neonate with an omphalocele (42). 

Congenital hypothyroid disorders occur with a frequency of one in every 4000 live births (pp. 144—145). If diagnosed at an early age. replacement thyroid hormone can be given and normal development can occur. Delays in treatment result in cretinism (see p. 144). Elevated T.SH, measured in blood spots, is diagnostic of disorders of the thyroid itself, i.e. primary neonatal hypothyroidism. The TSH screening test does not pick up pituitary dysfunction in the newborn. 

Tabie 50.9 Percentage of normal thyroid function and incidence of hypothyroidism in newborns with iodine excess due to angiocardiography in the neonatal period... 

Note The fetus and neonate are both at risk of developing iodine-induced hypothyroidism. Many cases of hypothyroidism in newborns have been reported, especially in iodine-deficient regions of Europe, but also in iodine-sufficient areas. 

There are many reasons why fetuses and newborn infants are more hkely to develop hypothyroidism due to iodine-containing pharmaceuticals. The abihty of the thyroid gland to escape from acute inhibition is defective in the fetus and neonate (Theodoropoulos et al, 1979), so both fetuses and newborns are sensitive to iodine overload. Also, the capacity to synthesize and release thyroid hormones is low in preterm babies (Ares et al, 1997). 

Iodine is readily absorbed when PVP-I is applied to the skin of a newborn infant, because of high cutaneous permeability, and neonates are very sensitive to iodine overload, as described previously. Topical PVP-I therapy is associated with a significant risk of hypothyroidism in neonates, especially very-low-weight babies (Smerdely et ai, 1989). Many cases of hypothyroidism induced by topical use of PVP-I have been reported in newborn infants, mainly from iodine-deficient regions (Markou et ai, 2001). However, a case of severe hypothyroidism in a neonate was also reported from North America, an iodine-sufficient region (Khashu et al. 2005). A premature infant developed severe hypothyroidism that required L-thyroxine replacement therapy after application of PVP-I for 20 days. 

Administration of contrast media, as well as PVP-I, is liable to cause hypothyroidism in neonates, especially in preterm babies. Two out of 24 term newborns and 6 out of 8 preterm infants developed hypothyroidism after radiological studies (I AHemand et aL, 1987). 

In China, a recent study in normal pregnant women detected a high percentage of antithyroid antibodies during pregnancy 47% in the first, 39% in the second and 16% in the third trimester. However, when the cut-off was modified, only 3.9% of the women had thyroid antibodies (Panesar et al., 2006). Another autoimmune cause able to provoke hypothyroidism is due to TSH receptor inhibiting antibodies (TSBAb), but unlike Hashimoto s thyroiditis, it is very rare (Arikawa et al., 1995). TSBAb cross the placenta and can cause fetal and neonatal hypothyroidism with an incidence estimated at 1/180000 newborns (Brown etal., 1996). 

In conclusion, important progresses are taking place in the standardisation of the survey methods used in IDD evaluation. At the same time new developments such as the introduction of thyroid echography improves the reliability of goitre prevalences assessment but international norms and directives will be needed for the presentation of these new data. With borderline low iodine intake, the percentage of recalled newborns obtained in neonatal screening for neonatal hypothyroidism is a sensitive index of the severity of the iodine deficiency. In former East of Europe where the... 

The concept of hypersensitivity of the newborn to the effects of iodine deficiency has developed since the introduction of systematic neonatal screening for congenital hypothyroidism. Hypersensitivity was initially documented in conditions of extreme iodine deficiency in developing countries and was subsequently confirmed in areas with marginally low iodine intake, including in Europe. 

Few countries in Europe are severely iodine deficient, but many, perhaps a majority, have a marginal iodine intake varying from 50 to 100 pg/day. The first world conference on neonatal thyroid screening held in Quebec in 1979 showed that, although the incidence of permanent sporadic congenital hypothyroidism in the newborn was similar in North America and in Europe, i.e. around 1/4000 live births, the incidence of transient primary hypothyroidism was almost six times higher in Europe... 

The first one is the observation that in areas with persisting borderline iodine deficiency, transient hypothyroidism in the newborns and also some anomalies of thyroid func on in pre iant women can still be linked to such an easily preventable factor as iodine deficiency. In some of these areas it is now clear that in screening, for neonatal hypothyroidism, roughly 2 out of 3 newborns rec alled for abnormal thyroid hormone or TSH levels are false positive. Apart from the psycholomcal and economic al costs linked to the rectal proc ess per-se, this transient hypothyroidism might induce around birth, brain maturation retardation of unknown long term... 

The evaluation of the iodine nutritional status was based on the determination of iodine concentrations in a large series of casual urine samples. 1 In 196 infants from the Brussels area, the median urinary iodine concentration was 4.8 iig/100 ml, 53% of the values being below 5 flg/dl. The urinary excretion of iodine was estimated as 51 lg/day.This in turn, enhances the susceptibility of the newborn, and particularly the premature to transient neonatal hypothyroidism.l ... 

Screening for congenital hypothyroidism frequently shows transient abnormality of thyroid function. The newborn is very susceptible to iodide excess and in 70 % of the cases (1), the reason for transient hypothyroidism is iodine overload (2-3). A common cause may be X ray investigations with iodine products. Two newborns hospitalized in our Neonatal Intensive Unit presented with iodine overload from investigations, producing transient hypothyroidism. The hypothyroidism disappears with iodine elimination. In one case, the child were submitted at six months to another iodine overload without consequences. The thyroid tests show no change. Transient neonatal hyperthyrotropinemia may be due to iodine overload, and the search for its etiology is essential, because it allows one to stop the treatment. 

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