Thyroid function in term newborn infants with congenital goiter

Iodine nutrition in Sudan: determination of thyroid-stimulating hormone in filter paper blood samples

In this study we examined the technique of measuring thyroid-stimulating hormone (TSH) on filter paper blood samples for use in evaluating the iodine nutrition status of newborns and adults living in iodine-deficient areas. Filter paper blood samples were obtained between the 5th and 7th day after birth from 103, 43 and 103 term newborns living in Khartoum (mild iodine deficiency), Kosti (moderate iodine deficiency) and Darfur (severe iodine deficiency), respectively. TSH was measured with a commercial assay and the levels were compared with those obtained with the same method in 1147 samples from term Swedish newborns, obtained on the 3rd to the 5th day of life. The mean (95% confidence interval) TSH levels of the three Sudanese groups and the Swedish group were 7.1 (4.8-9.4), 8.3 (6.6-10.1), 11.9 (0.9-22.9) and 4.51 (3.8-5.3) mU l-1, respectively. The mean TSH for all three Sudanese groups was higher than the Swedish mean (p < 0.001). TSH levels determined in filter paper blood samples from adults living in an iodine-deficient area showed a correlation (p < 0.001; r = 0.55) to levels in corresponding serum samples (range 0.52-14.1 mU l-1, median 3.4 mU l-1). No significant correlation was found, however, between blood spot levels and serum levels within the reference range (< 5 mU l-1). A modification of the commercial procedure consisting in using three instead of two monoclonal antibodies did not sufficiently improve the assay for measurements of TSH within the reference range. Thus, there is a need to develop the filter paper technique further to make it a useful test for monitoring iodine deficiency in populations expected to have TSH levels close to the reference range. In the examination of neonates, however, with their birth-induced surge of TSH, the current assay promises to be a convenient tool for discovering iodine deficiency within a community.

Serum levels of thyrotropin, thyroxine, 3,3',5-triiodothyronine and 3,3',5'-triiodothyronine (reverse T3) in the first six days of life

Serum concentrations of thyrotropin (TSH), thyroxine (T4), 3,3',5-triiodothyronine (T3), and 3,3',5'-triiodothyronine (rT3) were determined in blood samples from 140 full-term healthy newborns, 110 appropriate weight and 30 large-for-gestational age, aged 1 to 6 days, delivered vaginally and breast-fed. Serum TSH levels decreased progressively from the 1st to the 4th day; serum T4 levels increased, with a peak on the 2nd day, and then progressively decreased until the 6th day; serum T3 levels increased to a maximum value on the 2nd day and then decreased to a minimum on the 5th day; serum rT3 levels increased during the 1st day and the level remained constant from the 2nd to the 4th day and later decreased slightly. The decrease of T3 was more pronounced than that of T4, while rT3 remained at high levels until the 4th day. Dividing the data into narrower intervals of time, it was possible to show that the maximum value of TSH was followed first by a net increase in serum T3, then in T4, and lastly in rT3 ant T3 levels. These data indicate that the rapid increase after birth of serum T3 levels is prevalently TSH-dependent; the following increase in serum levels of T3 and the increase in rT3 are prevalently T4-dependent. This study provides data concerning physiological changes in TSH and thyroid hormones in serum from a large number of infants, during the first week of life. They should be useful for the understanding of thyroid function in early postnatal life.

Pituitary-thyroid responsiveness to thyrotropin-releasing hormone in preterm and small-for-gestational age newborns

A dose of 40 microgram TRH was injected intravenously in 12 preterm (PT) and 15 small-for-gestational age (SGA) babies (with advanced gestational ages) between 5 and 167 hours after birth. Serum-thyrotropin (TSH) was measured prior to and 30 and 180 min after TRH; serum-thyroxine (T4) and serum-triiodothyronine (T3) were measured prior to and 180 min after TRH. The percentage increase in serum-TSH in PT and SGA babies was comparable to that of fullterm newborns. The serum-TSH 30 min after TRH in SGA newborns was significantly correlated to basal TSH values, such a correlation could not be shown in the preterms. One SGA and four PT babies had a repeat TRH-test performed later in infancy: In all but one PT with a gestational age of 27 weeks the TSH rise was lower than in the neonatal period. The thyroid hormone responses after TRH were similar in the two groups of babies. The percentage increase above basal levels were: Median serum-T3 increase about 46% and median serum-T4 increase about 14%. It is concluded that in low-birth-weight newborn babies the pituitary TSH response to exogenous TRH was like that detected in fullterm newborns and more pronounced that later in infancy. The effect of endogenous TSH as measured by thyroid hormone increases was of the same magnitude as observed in fullterms and in adults.

Thyroid function in neonatal hypothyroidism

Various aspects of the thyroid function have been measured in 28 cases of neonatal hypothyroidism detected by means of the Quebec Screening Program for Metabolic Diseases. In all instances the T4 value in the blood of filter paper spot was below 2 SD of the mean of the day, averaging 0.39 +/- 0.04 ng/40 mul (mean +/- SEM) of eluted blood. The T4 value of a second similar sample averaged 0.22 +/- 0.04 ng/mul of eluted blood; this value was significantly lower than the first one. The serum T4 concentration was decreased in all the infants, whereas three of them had a normal serum TSH concentration. At least three groups of patients could be identified: (1) patients with primary thyroid failure, (2) those with secondary or tertiary hypothyrodism, and (3) those with abnormal synthesis of thyroid hormone.

Thyrotropin response to thyrotropin-releasing hormone in fullterm, euthyroid and hypothyroid newborns

The serum concentration of thyrotropin (TSH) and the TSH response following thyrotropin-releasing hormone (TRH) were studied in 16 euthyroid babies from 16 to 172 hours after birth and in 2 primary hypothyroid babies, 3 and 28 days of age. Serum-TSH was measured before an intravenous injection of 40 mug TRH and after 30 and 180 min. In the euthyroid babies increased basal levels of TSH were seen shortly after birth, followed by a pronounced decline. The extent of TSH increase after TRH could be correlated with the basal levels, and the relative increase was comparable to that which occurs in adults. In the hypothyroid babies very high basal levels of serum-TSH were seen, 125 and 400 muU/ml respectively, with no further increase following TRH stimulation. It was concluded that in euthyroid fullterm newborn, the relative response of serum-TSH to TRH was equal to that of adults, in spite of elevated thyroid hormone concentrations. In the hypothyroid newborn very high levels of serum-TSH were seen and a supplementary TRH-test seems without diagnostic value in congenital hypothyroidism.