High Incidence of Thyroid Dysfunction in Preterm Infants

Abstract

To determine the validity of a repeat thyroid function test for preterm infants, and to investigate factors that influence thyroid function of preterm infants, thyroid functions of 105 infants born at <32 weeks' gestational age were evaluated. Initial serum free thyroxine (fT4) and thyrotropin (TSH) levels were measured during the first 10 days of life, and repeated tests were performed more than 2 weeks apart. We analyzed the effects of gestational age, systemic diseases, and nutrition on the development of thyroid dysfunction. Thirty-one infants (30%) had low fT4 levels (<0.7 ng/dL) in the absence of elevated TSH levels (<7 µU/mL). Thirteen infants (12%) had hypothyroidism (fT4 <0.7 ng/dL, TSH ≥10 µU/mL) and mean age at diagnosis was 28±17 days. Twelve infants had moderately elevated TSH (TSH 10-30 µU/mL) with normal fT4 levels after 1 week of postnatal life. The history of undergone surgical procedure which needed iodine containing disinfectants was significantly frequent in the infant with hypothyroidism and transient TSH elevation. Repeated thyroid function tests are necessary for preterm infants, even though they initially show normal thyroid function, and are especially important for infants who have been exposed to excessive or insufficient levels of iodine.

Newborn screening for congenital hypothyroidism in very‐low‐birth‐weight babies: the need for a second test

“…Among 11 VLBW infants with permanent primary hypothyroidism, one was missed on the first screen. A compelling case for further sampling is presented in a recent study from Korea (Chung et al 2009). The authors performed serum thyroid function tests during the first 10 days of life and then on three subsequent biweekly intervals on 105 preterm infants, diagnosing 13 with hypothyroidism of whom 8 would have been missed on the initial sample.…”

Adrenal and thyroid function in the fetus and preterm infant

“…The estimated incidence of delayed TSH elevation is up to 12% in preterm infants63,64). Although the timing of this elevation varies, it usually develops between 2 and 6 weeks of age in most cases.…”

Incidence and Risk Factor of Permanent Hypothyroidism in Preterm Infants

“…Four infants were lost to follow up, and two infants were excluded because they were diagnosed with persistent CH caused by agenesis of the thyroid gland, as confirmed by thyroid ultrasound and 123 I radionuclide imaging. And 26 infants were excluded because of earlier trail off-therapy or stopping medication by self without medical suspension [9]. Finally, 49 infants were eligible for trial off-therapy at 36 months of age.…”

“…Especially, transient thyroid dysfunction is more commonly observed in preterm infants [9,10]. Therefore, more many infants are subjected to thyroid hormone supplementation than full term infants and a considerable portion of these prematurity can stop the thyroxine medication.…”