[Prospective study at 1 week of life of thyroid function in 97 consecutive pre-term newborns under 32 weeks of...

Hypothyroxinemia of prematurity (HTOP) is associated with neurodevelopmental impairment in pre-term newborns born at less than 32 weeks of gestation (WG). HTOP is not clearly defined in the literature and there is no consensus on whether or not treatment of HTOP is beneficial.

To describe the epidemiologic characteristics of HTOP and to determine the population at risk of HTOP.

Ninety-seven pre-term newborns under 32 WG were prospectively included in this study. FT4 and thyroid-stimulating hormone (TSH) serum levels were assessed between day of life 5 and 7. HTOP was defined as serum level of FT4 0.80 ng/dl or less and TSH less than 20 mUI/l.

The HTOP incidence was 29% in pre-term newborns under 32 WG and 64% in pre-term newborns 28 WG or less. FT4 levels were correlated with gestational age (P<0.001). The incidence of hypotension (61% vs 33%; P<0.05), patent ductus arteriosus (50% vs 17%; P<0.05), dopamine treatment (39% vs 16%; P<0.05), and hydrocortisone treatment (25% vs 6%; p<0.05) was higher in the HTOP group. Similarly, severe intracerebral hemorrhage (14% vs 0%; P<0.01) and hypothermic events under 36 °C (1.8 ± 1.7 vs 0.0 ± 0.4; P<0.05) were higher in the HTOP group.

Incidence of HTOP is high in pre-term newborns born at less than 28 WG. Morbidity during the first week of life is higher in cases of HTOP. Whether or not treatment of all pre-term with l-thyroxin is beneficial is unknown. However, treatment of the subgroup of pre-term newborns under 28 WG with HTOP should be considered.