Thyroid function in very-low-birth-weight infants with intraventricular hemorrhage

The objective of this investigation was to study the natural course of thyroid function in infants with intraventricular hemorrhage (IVH). A cohort of infants < 1,500 grams birth weight, n=247, were included in the analysis. Total T4 and thyrotropin from newborn screening during the 1st week of life (Test 1) and from repeat screening at 2-4 weeks postnatal age (Test 2) were compared in infants with IVH (n=43) and a group of infants without IVH. Fifty-nine percent of infants still had transient hypothyroxinemia at the time of Test 2. After multivariate analysis, infants with IVH had an increased odds of having a T4 < or = 6 microg/dL on Test 1 (OR 2.8, 95% CI 1.2-6.5), but at the time of Test 2 IVH was not associated with an increased odds of having a low T4. Only gestational age (OR 1.6, 95% CI 1.1-2.5) remained associated with an increased odds of having an extremely low T4 (< or = 4 microg/dL) at this time. Transient hypothyroxinemia remains common at 2-4 weeks of age in preterm infants. IVH is not independently associated with having a low T4 at this time.     

Thyroid status in the newborn infant: Effective thyroxine ratio and free thyroxine index

The effective thyroxine ratio (ETR) was determined in 28 term and 17 premature infants at birth and in 17 infants aged 0 to 6 weeks. The mean values found were significantly higher than those in 20 adult euthyroid controls. Serum thyroxine (T₄), T₃ resin uptake ratio (T₃ RUR), free thyroxine index (FTI), and ETR were determined in 14 term infants at birth. It was concluded that the raised T₄ was partly due to an increase in thyroxine binding globulin but that there was also a degree of true thyroid hyperactivity. Serum thyroxine alone was not considered a suitable index of thyroid function in infants and the free thyroxine index or the effective thyroxine ratio was preferred instead.     

Thyroid function in healthy premature infants.

Thyroid function was studied in healthy premature and term infants between 12 hours and 3 months of age. T4 and FT4I followed parallel courses in both groups; during the first 45 days, however, the values were significantly lower in premature infants under 34 weeks' EGA than in term infants (P less than 0.001). The post-delivery peak in TSH concentration (mean +/- SD) was 71.8 +/- 19.2 microunits/ml in the premature infants. In five premature infants, injection of TRH elicited a TSH increment of 29.4 +/- 20.7 microunits/ml at 30 minutes. T3 concentration was not significantly different in premature and term infants.     

Serum thyroxine and triiodothyronine levels in newborns: effect of gestational age

Serum T₄ and T₃ were measured in 31 newborns of gestational ages 32–43 weeks. Out of 31, 11 were term, 12 preterm and 8 postterm. Blood samples were taken from cord blood and from peripheral vein at 24 and 72 hours of age. Serum T₄ and T₃ values were low in cord blood samples, raised in 24 hours samples and then declined in 72 hour samples. In pretern newborns cord T₄ and T₃ values were significantly lower and there was a blunted rise and fall in 24 and 72 hours samples as compared to term newborns. In post term newborns cord serum T₄ and T₃ values were significantly raised while in peripheral vein samples difference was statistically insignificant as compared to term newborns. This high incidence of low cord values and transient hypothyroxinemia observed in preterm and postnatal surge of T₄ may give rise to false results while screening for hypothyroidism.     

Effect of phototherapy on thyroid stimulatory hormone and free thyroxine levels

Objective : To study the effect of phototherapy for neonatal hyperbilirubinaemia on thyroid function as neonatal thyroid screening is sometimes performed during exposure to phototherapy. Methodology : Infants with non-haemolytic hyperbilirubinaemia were sequentially allocated to fibre-optic phototherapy, conventional daylight phototherapy, or a combination of both. Bilirubin concentration was monitored 12 hourly by capillary blood sampling; venous blood was sampled for thyroid stimulating hormone (TSH) and free thyroxine (fT₄) determinations, at start of exposure, at 24 h, end of exposure and 1 day later. Comparable unexposed infants served as controls. Results : All 123 study infants and 25 controls remained well during the study. Bilirubin levels declined during phototherapy, being most rapid in the combination group. The TSH and fT₄ values at start of exposure were 3.86 ± 0.41 mU/L (mean ± SEM) and 33.20 ± 1.16 pmol/L, respectively, in the fibre-optic group, 3.62 ± 0.38 mU/L and 37.22 ± 1.76 pmol/L in the daylight group, and 4.40 ± 0.48 mU/L and 29.91 ± 1.13 pmol/L in the combined group, compared with 5.77 ± 0.40 mU/L and 34.46 ± 1.68 pmol/L in the control group. The TSH and fT₄ values declined with increasing age in the phototherapy and control groups with end of exposure values of 2.90 ± 0.28mU/L and 27.71 ± 0.71 pmol/L, 2.77 ± 0.31 mU/L and 33.52 ± 1.22pmol/L, and 3.44 ± 0.30 mU/L and 27.54 ± 0.88 pmol/L, respectively, compared with 4.21 ± 0.61 mU/L and 27.19 ± 2.33 pmol/L (at 72 h) in the control group. The pattern of TSH and fT₄ decline in the exposed and control groups was similar, being related to increasing age. Conclusions : The validity of neonatal thyroid screening is not affected by fibre-optic or conventional phototherapy or by both combined.     

Behavior of the levels of free triiodothyronine, triiodothyronine, free thyroxine, thyroxine, thyrotropin and thyroxine-binding globulin in the serum of children with nephrotic syndrome

Concentrations of free triiodothyronine, triiodothyronine, free thyroxine, thyroxine, thyrotropin, thyroxine-binding globulin, urea, creatinine, cholesterol and total protein were determined in serum of four children (ages from 8 to 16 years) with nephrotic syndrome undergoing therapy. The results showed that at serum protein concentration of less than 4.5 g/dl the concentration of free thyroxine was 3.35 +/- 2.32 pg/ml and that of free triiodothyronine 2.65 +/- 0.96 pg/ml. Elevation of the protein concentration to 4.5-5.7 g/dl lead to an increase in the concentration of free thyroxine to 6.53 +/- 3.69 pg/ml and of free triiodothyronine to 3.32 +/- 1.08 pg/ml. The age-matched reference values for free thyroxine are 15.72 +/- 1.9 pg/ml and for free triiodothyronine 5.10 +/- 1.29 pg/ml. The concentration of thyroxine, triiodothyronine and thyroxine-binding globulin were decreased whereas that of thyrotropin was elevated. Although free triiodothyronine and triiodothyronine were decreased they remained close to the normal range thus preventing apparent hypothyroidism. Improvement in the concentration of serum protein and cholesterol lead to an improvement of serum levels of thyroid hormones and thyroxine-binding globulin; concentrations of thyrotropin remained elevated.     

Serum concentrations of growth hormone, insulin, free thyroxine, thyrotropin, and cortisol in very-low-birth-weight infants receiving total parenteral nutrition

Serum concentrations of growth hormone, insulin, free thyroxine, thyrotropin, cortisol, and glucose were measured during four time periods (0 to 4, 5 to 11, 12 to 18, and greater than or equal to 19 days of life) in 16 mechanically ventilated very-low-birth-weight infants (mean [+/- SD] birth weight, 1017 +/- 196 g) receiving total parenteral nutrition and in 21 very-low-birth-weight infants not requiring mechanical ventilator support (mean [+/- SD] gestational age, 30 +/- 1.7 weeks; mean [+/- SD] birth weight, 1149 +/- 210 g) fed enterally. There were no significant differences in the serum concentrations of the hormones or in the glucose levels between the two groups at any time interval. Present data demonstrate no significant difference in the serum concentration of glucose, insulin, growth hormone, cortisol, free thyroxine, and thyrotropin between very-low-birth-weight infants fed enterally and those maintained on a regimen of total parenteral nutrition.     

Thyroid function in healthy normal,low birthweight and preterm infants

To delineate more precisely the role of gestational age, weight at birth and thyroid status at birth on the postnatal changes in thyroid hormone levels, serum T₄, T₃, TSH and in some cases FT3I were measured at birth and at 3–4 h, 24–30 h, 6–9 days and 13–20 days.Subjects studied were healthy appropriate-for-date (AFD) and small-for-date (SFD) term neonates and healthy AFD and SFD preterm children. At birth T₄ and T₃ are related to both gestational age and weight with T₄ and T₃ showing lower values in preterm and SFD term neonates than in AFD term children. After birth T₄ and T₃ concentrations show a better correlation with gestational age than with weight at birth.For TSH no correlation was found at birth, a positive correlation at 24–30 h, no correlation at 6–9 days and a negative correlation at 13–20 days both with gestational age and weight at birth. In term and close-to-term infants (36 weeks) individual T₄ levels at 6–7 days show a colse relationship with those at birth; in the younger children (34 and 35 weeks) lower T₄ values are found, despite equal cord blood values. The individual cord blood FT3I/TSH values correlate well with those at 6–7 days of age.It is concluded that after birth all children have changing T₄ and T₃ values, but the pattern and level are influenced by the maturity of the child and its thyroid status at birth measured by T₄ and by the FT3I/TSH ratio. Weight at birth influences T₄ at birth, but during the 1st week the weight of the child influences the T₄ and T₃ levels in only a minor way.Abbreviations AFD appropriate for date - SFD small for date - CHT congenital hypothyroidism     

Plasma levels of somatostatin and gastrin in sick infants and small for gestational age infants

Sick neonates often have a disturbed gastrointestinal motility. As somatostatin inhibits various gastrointestinal functions, we investigated whether or not somatostatin levels are high in sick infants. Somatostatin and gastrin levels were measured in plasma samples collected from sick and healthy neonates. Somatostatin levels were found to be significantly elevated in sick infants when compared to healthy ones, both term (91 versus 5 pM) and preterm (35 versus 5 pM). We suggest that the gastrointestinal symptoms seen in infants during illness may be related to an enhanced secretion of gastric somatostatin.     

Relationship between maternal thyroxine levels during pregnancy and memory function in childhood

Two investigations are reported into the memory functions of a group of subjects for whom information on maternal thyroxine (T4) levels during pregnancy is available. The first study made when the subjects were aged 14-15 years examined forward and backward memory span. No relationship between maternal T4 levels and capacity of the short-term store, measured as length of forward memory span, was found. Backward memory span, which involves performing a mental operation on the material held in store, was found to be associated with maternal T4 level. The second study, made when the subjects were aged 16-17 years, found a relationship between maternal T4 levels during pregnancy and memory for serial position. Findings are discussed in terms of the role of maternal thyroxine in fetal brain development.     

Assessment of behaviour on the Brazelton scale in healthy preterm infants from 32 conceptional weeks until full-term age

20 healthy preterm infants were assessed weekly by the Brazelton Neonatal Behavioural Assessment Scale from 1–2 weeks after birth until they reached their expected date of birth. The gestational age of the infants ranged from 28 to 34 weeks. Although the full scale could not be used before 36 conceptional weeks. obvious progress in development was found for most items of the scale. In particular there was improvement in orienting responses and in motor performance during the observation period. At full-term age comparisons were made with a group of normal-term infants (n = 80). All premature infants underwent standard neonatal neurological examination at full term, and tests of neurological function and psychomotor development up to the age of 18 months.     

Variations in the number of births by day of the week,and morbidity and mortality in very-low-birth-weight infants

Objective

To know the distribution of births of very low birth weight infants by day of the week, and whether this distribution affects the morbidity and mortality in this group of patients.

Direct assay of free thyroxine in the newborn

Several reagent sets are available, which allow a direct assay without dialysis of the free, bioavailable part of total thyroxine in plasma. A methodological investigation showed that the solid phase (coated tubes) kit from Clinical Assay gives reproducible results in plasma volumes of 50 microliter. Plasma samples from 95 newborns have been assayed at the 4th to 5th day of life. The mean concentration for free thyroxine of 62 infants born at term was 17 pmol/l with a log 2 SD range of 10-28 pmol/l. This value is similar to the normal value in adults (15.1 pmol/l, log 2 SD range 8.3-27.4 pmol/l). This is in contrast to the total T4 concentration: mean value for newborns 182 nmol/l (normal range 2 SD log 130-250 nmol/l) compared to a mean of 90 nmol/l (normal range 2 SD log 51-157) for adults. Mean free T4 concentration was 11.5 pmol/l in 18 premature infants (gestational ages 34-35 weeks: mean 8.7 pmol/l; gestational ages 36-37 weeks: mean 15.3 pmol/l). The lowest concentrations were found in infants with a respiratory distress syndrome: mean 8.9 pmol/l. TSH did not exceed 10 mU/l. It is concluded that the method used allows a direct estimation of free T4 in small plasma samples and allows a rapid decision in suspected thyroid disorders in infants.     

Postnatal changes in proximal and distal tubular sodium reabsorption in healthy very-low-birth-weight infants

We studied 7 healthy very-low-birth-weight male infants with a mean birth weight of 1,195 g and a gestational age of 29.0 weeks, from birth to 6 weeks. The filtered Na load increased fivefold but urine Na excretion decreased from 3.4 to 0.1% of the filtered Na load. The efficiency of Na reabsorption increased 8% in the proximal tubule compared with 66% in the distal tubule. Because greater than 90% of Na reabsorption always occurred proximally, the smaller percentage increase in efficiency of the proximal tubule contributed as much as the larger percentage increase in efficiency of the distal tubule to the postnatal improvement in renal Na conservation.