Detection Of Thyroid Function And Evaluation Of Intervention Effects In Preterm Infants

Objcetive:To explore the reference range of thyroid function by measuring thyroid hormone levels in preterm infants based on gestational age from 7 to 10 days after birth.By evaluating the efficacy of levo-thyroxine（L-T4）replacement therapy in transient hypothyroxinemia of prematurity（THOP）and some hyperthyrotropinemia（HT）of preterm infants,and following up the outcome of them,we expect to provide some reference for the diagnosis and treatment of thyroid dysfunction in premature infants.Method:A total of 363 preterm infants admitted to the Department of Neonatal Intensive Care Unit in our hospital from September 2017 to January 2019.They were divided into three groups based on gestational age:28-30⁺⁶ weeks,31-33⁺⁶ weeks,and 34-36⁺⁶ weeks.Blood serum was collected and chemiluminescence immunoassay were used to measure thyroid hormone levels in preterm infants born 7-10 days.The selected parameters of thyroid function were free triiodothyronine（FT3）,free thyroxine（FT4）,triiodothyronine（T3）,thyroxine（T4）,and thyroid stimulating hormone（TSH）.Patients with confirmed THOP and HT（6.0<TSH<15.0mU/L）among these preterm infants were divided into treatment group and control group randomly.The treatment group were given L-T4,while the control group did not get L-T4 for treatment.Early clinical recovery（duration of hospital stay,duration of jaundice,duration of intravenous nutrition,time to regain birth weight）,physical and mental development assessment（head circumference,body length,weight,Gesell Development Scale）were compared respectively between the two groups when they reached the correction age of one year.Results:1.The levels of T3,T4,FT3,and FT4 were positively correlated with gestational age（p<0.05）,and the correlation coefficients were r（T3）=0.489,r（T4）=0.539,r（FT3）=0.510,and r（FT4）=0.468 respectively.There was no correlation between TSH and birth gestational age（p>0.05）.2.The levels of T3,T4,FT3 and FT4 were statistically significant among different groups（P<0.05）.Reference intervals for thyroid function parameters of T3（ng/dL）,T4（ug/dL）,FT3（pmol/L）,and FT4（pmol/L）in preterm infants were as shown:28-30⁺⁶ weeks:[43.62--127.76],[2.78—10.89],[1.57--4.95],[7.49--17.53];31-33⁺⁶weeks:[48.91--135.42],[3.77--11.53],[2.14--5.79],[8.37--19.98];34-36⁺⁶weeks:[58.76--141.20],[4.47--12.23],[3.13--6.23],[10.89--21.13]seperately.There was no significant difference in TSH levels among different gestational age groups（P>0.05）,and the reference interval of TSH level was 0.93--13.90mU/L.3.69 cases（19.0%）of THOP were diagnosed,including 35 in the treatment group and34 in the control group.And in the control group,28 patients（82.35%）recovered before the correction age of 3 months.The early clinical recovery,physical and mental development assessment in the treatment group were better than those in the control group after one year of treatment（p<0.05）.4.64 cases（17.63%）with TSH<15.0mU/L of HT were diagnosed,including 32 in the treatment group and 32 in the control group.In the control group,26 patients（81.25%）recovered before the correction age of one year.There was no statistically significant difference in the early clinical recovery,physical and mental development assessment after one year between the two groups（p>0.05）.Conclusions:1.Thyroid function of premature infants is positively correlated with gestational age.A reference interval of thyroid function for preterm infants needs to be developed based on gestational age.2.Most preterm infants with THOP can recover within the correction age of 3 months spontaneously.Timely L-T4 replacement therapy is beneficial to them.3.Most preterm infants with TSH<15.0mU/L of HT can recover within the correction age 1 year spontaneously.L-T4 replacement therapy was not found significant positive effect on them.It should be given comprehensive consideration when choosing drug therapy.