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Clinical indicators that influence a clinician's decision to start L-thyroxine treatment in prematurity with
Aslan Yilmaz1, Yavuz Ozer2, Nesrin Kaya3
1Department of Neonatology, Cerrahpasa Faculty of Medicine, Istanbul University-Cerrahpasa, Kocamustafapasa, Fatih, Istanbul, 34098, Turkey. draslanyilmaz@hotmail.com.
Insights
Transient hypothyroxinemia of prematurity (THOP) affects nearly half of preterm infants, with lower gestational age and birth weight increasing its prevalence. As gestational age decreases, more infants with THOP require levothyroxine (L-T4) treatment, often due to associated comorbidities.
Area of Science:
- Neonatal Medicine
- Endocrinology
- Pediatrics
Background:
- Transient hypothyroxinemia of prematurity (THOP) is characterized by low circulating thyroxine (T4) with normal or low thyroid-stimulating hormone (TSH).
- This condition is observed in preterm infants, necessitating evaluation of its incidence and management.
Purpose of the Study:
- To determine the incidence of THOP in preterm infants.
- To analyze the clinical and laboratory findings associated with THOP.
- To evaluate the outcomes of levothyroxine (L-T4) treatment in affected infants.
Main Methods:
- Thyroid function tests were performed on 181 preterm infants (24-34 weeks gestation) between postnatal days 10-20.
- Infants were categorized based on gestational age (GA) and compared for clinical and laboratory characteristics.
- Patients with THOP were compared with and without L-T4 treatment.
Main Results:
- THOP incidence was 45.8%; 47.5% of infants were euthyroid.
- Infants with THOP had significantly lower mean birth weight and GA (p<0.001).
- L-T4 treatment was initiated in 43% of THOP infants, with higher rates in earlier gestations (p<0.001). Treated infants had more comorbidities.
Conclusions:
- THOP prevalence is inversely related to gestational age and birth weight.
- Lower gestational age correlates with an increased need for L-T4 treatment in THOP patients.
- Comorbidities are associated with a higher requirement for L-T4 treatment in preterm infants with THOP.
Background:
Transient hypothyroxinemia of prematurity (THOP) is defined as a low level of circulating thyroxine (T4), despite low or normal thyroid-stimulating hormone (TSH) levels.
Aims:
We aimed to evaluate the incidence of THOP, the clinical and laboratory findings of preterm infants with this condition and the levothyroxine (L-T4) treatment.
Methods:
Preterm infants (n = 181) delivered at 24-34 weeks of gestation were evaluated by their thyroid function tests that were performed between the 10th and 20th days of postnatal life and interpreted according to the gestational age (GA) references. Clinical and laboratory characteristics of the patients with THOP and normal thyroid function tests were compared. Patients with THOP and treated with L-T4 were compared with the ones who were not regarding laboratory, and clinical characteristics.
Results:
Incidence of hypothyroxinemia of prematurity was 45.8% (n = 83). Euthyroidism, primary hypothyroidism, and subclinical hypothyroidism were diagnosed in 47.5% (n = 86), 5% (n = 9) and 1.7% (n = 3) of the patients, respectively. Mean birth weight (BW) and GA were significantly lower in the hypothyroxinemia group than in the euthyroid group (p < 0.001). L-T4 was started in 43% (n = 36) of the patients with THOP. Treatment initiation rate was 44.4% (n = 16) in 24-27 wk, 41.6% (n = 15) in 28-30 wk, and 13.8% (n = 5) in 31-34 wk. As the GA increased, the incidence of THOP and the rate of treatment initiation decreased (p < 0.001). The lowest free thyroxine (FT4) cut-off value was 0.72 ng/dl in the treated group. In addition, incidences of vancomycin + amikacin, caffeine, dopamine treatments, RDS, IVH, BPD, central catheter, FFP transfusion, and ventilator support were higher in the treated group (P < 0.05).
Conclusion:
This study revealed that prevalence of THOP increased as the GA and BW decreased. As the GA decreased, THOP patients requiring L-T4 treatment increased. Additionally, association with comorbid diseases increased the requirement of treatment.
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