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Neonatal hypothyroxinemia: effects of iodine intake and premature birth
S Ares1, H F Escobar-Morreale, J Quero
1Unidad de Neonatología, Hospital La Paz, Instituto Nacional de Salud, Madrid, Spain.
Insights
Preterm infants often experience iodine deficiency, impacting thyroid hormone levels crucial for brain development. Even with adequate intake, preterm babies may have lower thyroid hormone levels than term infants.
Area of Science:
- Neonatalogy
- Endocrinology
- Nutritional Science
Background:
- Iodine is essential for thyroid hormone synthesis, critical for fetal and neonatal development.
- Preterm infants have unique physiological challenges affecting nutrient balance and hormone regulation.
- Thyroid hormone status is vital for neurodevelopment, especially in premature infants.
Purpose of the Study:
- To investigate iodine (I) intake, urinary excretion, and thyroid hormone profiles in preterm (PT) versus term (T) neonates.
- To determine the impact of iodine intake and prematurity on thyroid hormones (T4, FT4, T3, TSH, Tg) up to 2 months postpartum.
- To assess the relationship between iodine balance and thyroid function in early neonatal life.
Main Methods:
- Comparison of urinary iodine excretion and serum thyroid hormone levels (T4, FT4, T3, TSH, Tg) between preterm and term neonates.
- Assessment of iodine balance (intake vs. excretion) in the first two months of life.
- Analysis of the influence of postmenstrual age, iodine intake, and prematurity on thyroid hormone status.
Main Results:
- Preterm infants, especially those very premature and sick, were in negative iodine balance initially.
- A significant portion (75-80%) of ingested iodine was unaccounted for in urine for both PT and T neonates.
- Low iodine intake negatively impacted serum FT4, T3, Tg, and TSH in PT neonates, independent of age.
- Preterm birth itself negatively affected T4, FT4, and Tg for 6-8 weeks, irrespective of iodine intake or age.
- Thyroid hormone levels (T4, FT4, T3) increased with postmenstrual age, while Tg decreased; TSH remained unchanged.
Conclusions:
- Urinary iodine levels do not accurately reflect iodine intake in neonates.
- Preterm infants are at risk for iodine deficiency, negatively affecting thyroid function and potentially neurodevelopment.
- Even with adequate iodine intake, preterm infants exhibit lower thyroid hormone levels compared to term infants during a critical brain development period.
- Interventions mimicking the intrauterine hormonal environment may be beneficial for preterm infants' maturation and development.
Abstract:
We have investigated the effects of iodine (I) intake on urinary I excretion in preterm (PT) babies up to 2 months after birth and its effect on serum T4, free T4 (FT4), T3, TSH, and thyroglobulin (Tg) levels compared to those in term (T) newborns. Very premature and very sick infants were in negative I balance for the first weeks after birth. Later, these same infants, as well as the other PT and T newborns, were in positive balance; 75- 80% of the ingested I was not accounted for in the urine. The urinary I levels of PT and T neonates cannot be equated to their I intakes. T4, FT4, and T3 levels in PT and T neonates increased with postmenstrual age, whereas Tg decreased and TSH did not change. Serum FT4, T3, Tg, and TSH levels in PT neonates were affected negatively, independently from age, by a low I intake. PT birth also affected T4, FT4, and Tg negatively, independently from I intake and postmenstrual age, for at least 6-8 weeks after birth. Care should be taken to avoid I deficiency in PT neonates. However, even when I intake is adequate, PT newborns are hypothyroxinemic compared to T babies during an important period of brain development. This suggests the possible convenience of interventions that might mimic the intrauterine hormone environment and accelerate maturation.