Incidence and Risk Factor of Permanent Hypothyroidism in Preterm Infants

Abstract

Background: To investigate the incidence and risk factors of permanent hypothyroidism in premature infants diagnosed with congenital hypothyroidism. Methods:A retrospective review of medical records of preterm infants was performed between March 2010 and December 2013. We included infants who were treated with thyroxine after being diagnosed with congenital hypothyroidism and persistent hyperthyrotropinemia. Exclusion criteria included an infants who were lost to follow up or earlier discontinuation of thyroxine medication and had proven permanent hypothyroidism. We performed trial offtherapy at 36 months of age.Results: A total of 49 infants were eligible for trial off-therapy at age 3 years. Permanent and transient hypothyroidism was diagnosed in 12 and 37 infants, respectively. Persistent hypothyroidism was more frequent in the infants with high TSH and low FT4 levels at initial screening and high incidence in abnormalities in thyroid imaging work-ups and positive anti-thyroid antibodies. Moreover, the average thyroxine dosage during follow-up was significantly higher in infants with persistent hypothyroidism (p<0.05). Conclusion:Thyroid dysfunction is common in preterm infants, and nearly 80% of infants showed transient hypothyroidism. Therefore, if there is no other risk factor for permanent hypothyroidism, it is possible to consider an earlier trail off-therapy for preterm infants.

Transient hypothyroidism in the newborn: to treat or not to treat

“…In Korea, a total of 13 laboratories perform the NBS TSH, and the cutoff levels of TSH vary from 10.0 to 22.5 mIU/mL according to each laboratory protocol (8). Another recent study from Korea showed that nearly 80% of preterm infants with CH treated for 3 years with thyroxine were later diagnosed with transient hypothyroidism (9 (11). Infants with trisomy 21 (Down syndrome) have a higher incidence of hypothyroidism detected by NBS programs, occurring as commonly as 1:50 newborns but they rarely have transient hypothyroidism (12).…”

Serial Thyroid Function Test in Very Low Birth Weight Neonates

“…20,21 THT was found in 7.3% of VLBW neonates in our study as agreement to 16% in Armanian et al 8 Another study involving 622 preterm neonates found hyperthyrotropinemia with normal TSH in 35 (5.6%) neonates. 22 THT may be due to inability of the thyroid gland of premature infants to cope with external iodine overload, and thyroid function is more likely to normalize on re-evaluation. 13,23,24 Eleven (11.5%) neonates had delayed TSH rise at 4 weeks of age in our study.…”

Guideline for the treatment of hypothyroidism in prematurity

“…[ 1 ] The frequency of congenital hypothyroidism is high in preterm and low-birth-weight (LBW) newborns compared to normal ones due to insufficient development of the hypothalamic-pituitary axis (1/400 vs 1/4000). [ 8 9 ]…”

“…In most countries, this screening is conducted at the age of 2, 6, and 10 weeks, therefore, the normal TSH level in newborns with hypothyroidism cannot rule out the hypothyroidism. [ 9 10 16 17 18 ]…”

“…If the level of T4 is below 2 standard deviation of the mean, it can be considered abnormal. [ 9 ] Also, the normal value of free T4 in preterm infants based on gestational age in the first week after birth is 0.8–2.6 ng/dL. Owing to the low level of T4 in the first weeks after birth in premature neonates, the table is used to interpret the normal level of this hormone.…”