Serum thyroxine neonatal

Effects on the testis were evaluated in adult male rats that were neonatally exposed to either Aroclor 1242 ( iO, 40, or 80 mg/kg/day) or Aroclor 1254 ( 40 or 40 mg/kg/day) by daily subcutaneous injection from birth to PND 25 (Cooke et al. 1996). Examinations at 135 days of age showed significantly increased testis weight at 40 mg/kg/day Aroclor 1242 and 40 mg/kg/day Aroclor 1254, and increased daily sperm production at 10 mg/kg/day Aroclor 1242 and 40 mg/kg/day Aroclor 1254. Sertoli cell proliferation was also increased in exposed rats (only examined in 15-day-old pups treated with 40 mg/kg/day Aroclor 1242). Both Aroclor 1242 and 1254 also suppressed serum thyroxine (T4) concentrations and T4 replacement decreased or eliminated the testicular effects. As discussed in Section 3.2.2.8 (Endocrine Effects), other studies also indicate that hypothyroidism is involved in PCB-induced testicular effects in neonatal rats. Fertility tests showed that all Aroclor 1242-treated rats successfully impregnated unexposed females (Aroclor 1254 was not tested). 

Further data from Papua New Guinea indicates a relationship between the level of maternal thyroxine with the outcome of current and recent past pregnancies including mortality and the occurrence of cretinism. There were proportionally more perinatal (i.e., stillbirths and neonatal) deaths, and cretins, among the offspring of women who showed the lowest levels of serum thyroxine ... 

Iodine concentrations in breast milk and in random urine in neonates and the serum concentrations of neonatal TSH and free thyroxine on day 5 after delivery were measured after the use of povidone-iodine for disinfection after delivery (36). Iodine concentrations in the breast milk and neonatal TSH were significantly raised. Perinatal iodine exposure causes transient hypothyroidism in a significant number of neonates, in whom careful monitoring and follow-up of thyroid gland function are needed. It is better to avoid the use of iodine-containing antiseptics in pregnancy and neonates, especially if follow-up cannot be guaranteed. 

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). 

Graves disease may occur in the newborn infant, either due to passage of TSH-R Ab [stim] through the placenta, stimulating the thyroid gland of the neonate, or to genetic transmission of the trait to the fetus. Laboratory studies reveal an elevated free thyroxine, a markedly elevated T3, and a low TSH—in contrast to the normal infant, in whom TSH is elevated at birth. TSH-R Ab [stim] is usually found in the serum of both the child and the mother. 

Free Thyroxine. Measurement of free T4 radioimmunoassay in dried blood samples has been found to be useful to avoid false-positive results for low TBG in neonatal hypothyroid screening. Enzyme immunoassay of free T4 in serum was developed by Weetall et al. (W7) and subsequently by us (16). 

Iodine concentrations in breast milk and in random urine in neonates and the serum concentrations of neonatal TSH and free thyroxine on day 5 after dehvery were measured after the use of povidone-iodine for disinfection... 

Serum total T4 (TT4), FT4 and TSH levels of the neonates and serum total T3 (TT3), TT4 and TSH levels of their mothers were measured. All the neonates with hypothyroidism had hormonal findings that were diagnostic of hypothyroidism. After 8 weeks of thyroxine therapy, euthyroidism was achieved in all the hypothyroid neonates (Table 65.2). The borderline elevation of TSH levels, accompanied by increased TT3 and near-normal TT4 levels, indicated the presence of subcfinical hypothyroidism in the mothers of neonates with hypothyroidism (Table 65.3)... 

Note Neonates with hypothyroidism had increased TSH ieveis and decreased TT4 and FT4 ieveis when compared with age-matched heaithy neonates. After 8 weeks of thyroxine therapy, thyroid hormones returned to normai ieveis (NS nonsignificant p> 0.05] TSH thyroid-stimuiating hormone TT4 serum totai T4 FT4 serum free T4). 

A3. Abuid, J., Stinson, D. A., and Larsen, P. R., Serum triiodothyronine and thyroxine in the neonate and the acute increases in these hormones following delivery. J. Clin. Invest. 52, 1195-1199 (1973). 

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