Profile of umbilical cord blood TSH , T 4 and influence of perinatal factors on thyroid functions in Newborns

Background: Congenital Hypothyroidism, if not treated well in time, may be disastrous for growth and development of child ,therefore early detection of congenital hypothyroidism is important, either by TSH or T4, or both by newborn screening . Influence of several perinatal factors have to be considered while interpreting values of thyroid functions in newborns. The present study is to determine Umbilical cord blood TSH and T4 profile in Newborns and to study influence of Perinatal factors on Umbilical cord blood TSH and T4 . Methods: Umbilical cord blood samples were collected for assessment of TSH and T4 in 830 newborns. The influence of Perinatal factors such as gestational age ,weight, sex, mode of delivery, Ecclampsia, Ante partum haemorrhage , Birth Asphyxia ,Premature rupture of membranes and maternal HIV status on the newborns TSH ,T4 were analyzed . Results: Mean TSH and T4 levels between Pre term and Term and between Term and Post term was statistically significant .Whereas, only T4 level between Preterm and Post term ,was statistically significant . Mean TSH levels, when compared in babies with & without severe birth asphyxia was also statistically significant . Other perinatal factors did not affect cord TSH and T4 levels ,as it was not statistically significant . Conclusion: Perinatal factors have influence over values of Cord blood TSH and T4 levels and a caution in their interpretation should be considered .


Introduction
Congenital hypothyroidism is the commonest preventable cause of mental retardation and also thyroid disorders are most common among pediatric endocrinal problem 2 .In regions where iodine deficiency is severe, Most babies with congenital hypothyroidism appear normal at birth and show minimal evidence of thyroid deficiency.Clinical diagnosis is made in only 10% children in the 1 st month of life and 30% in the 1 st three months , hence there is a high risk of delayed diagnosis based on clinical examination alone.Early diagnosis and therapy improves the intellectual outcome and growth of the baby.Therefore screening of newborns is justified to prevent complication like Congenital Hypothyroidism.Many countries of western world have their own screening programmes ,where filter spot test for TSH and T4 are performed in newborns at 4-5 days after birth.In our country no such programme exists at national level.It is very difficult to call back newborns for follow up once they are discharged and probably high turn over of delivery rates in tertiary hospitals ,thus Cord blood sample is preferred for its ease, more practical for short hospital stay following delivery and thus is a practice in some Asian countries 3,4 .Fuse, et al 5 had shown that mixed cord blood is a good sampling technique for screening for CH.Indian academy of pediatrics recommended the use of cord blood for screening of Congenital Hypothyroidism 6,7 .However, using TSH alone for screening, though sensitivity is high but it has chances of high false positivity rates 8 .In addition Various perinatal factors such as gestational age ,weight, sex, mode of delivery, Eclampsia, APH, Birth Asphyxia ,PROM, HIV status, maternal age, etc. may influence cord blood TSH and T4 levels 7 9,10, 11, 12 .This study was performed to observe the influence of these perinatal factors and to decrease false positivity, both TSH and T4 were included in our study and to compare the mean values of cord blood TSH & T4 in relation to Gestational age and weight and to study the influence of perinatal factors on umbilical cord blood TSH & T4.

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conducted in the Deptt. of pediatrics, Surat municipal institute of medical education and research (SMIMER),Surat for a period of one year .Study was approved by Institutional ethical committee.Consent for blood samples were obtained from parents of Newborns.It was based on the cord blood sample obtained during this period.Those newborns whose mothers were on antithyroid drugs or newborns with congenital anomalies, syndromic features or malformations, those delivered outside the institute were excluded from the study.Ten ml of mixed umbilical cord arterial and venous mixed blood in sterile plain vacutte on the maternal side of cord , after ligation was carefully collected by attending resident doctor and was sent to the laboratory immediately.Serum was separated after centrifuging cord blood .Newborns were examined in detail after birth.Socio -demographic and other Data of both mothers and newborns were recorded and entered in predesigned Performa.Factors included for comparison were, weight ,gestational age, sex, Oxytocin ,APH, Pre Ecclampsia, HIV status of mother, Premature rupture of membranes and severe birth asphyxia.All newborns whose TSH report was found to be >20 MU/L and or T4 <6.5µg/dl were recalled after seven days for repeat TSH & T4 estimation for confirmation of Congenital Hypothyroidism.These cut offs were also used by other studies 2, 3, 7, 13, 14, 15,16 and as per AIIMS protocol 17 for diagnosing Congenital hypothyroidism.TSH and T4 assay was performed by chemiluminometric technology by ADVITA Centaur CP TSH assay Kit manufactured by Siemens Health care diagnostics Inc. Assay range for TSH was 0.010 -150 MU/L ,whereas, it was 0.3 -30 µg/dl for T4 assay.

Results
A total of 830 newborns were enrolled in the study out of which 290(34.9%) were pre terms ,380 were terms (45.78) and 160 (19.22) were post terms .In the preterm 207 were AGA and 83 were SGA.In term 268 (70.52) were AGA and 112 were SGA (29.47).In post term neonates 100 were AGA and 60 were SGA.Observed Range of TSH was 1.04-150 Mu/L in preterm ,1.09 -162 Mu/L in Term and 1.04 -20.98 Mu/L in Post Term respectively.Observed Range of T4 was 4-28 µg/dl ,2-25 µg/dl and 9 -28 µg/dl in pre term ,term and post term respectively.Percentile Umbilical cord blood TSH (mu/l) and T4(µg/dl) values according to Gestational Ages is mentioned in Table-1.On comparing, Mean TSH and T4 levels among Preterm ,Term and Post term newborns it was found that mean TSH levels between Pre term and Term newborns was statistically highly significant (p<0.001)whereas, T4 levels were also statistically significant (p<0.05).

Discussion
Although several Studies with Thyroid functions in newborns have been conducted, the exact incidence of congenital hypothyroidism in India is not known 2 .Data from various studies conducted show different incidences of congenital hypothyroidism varying from 1:248 to 1:2800 ( including north east India). 3,13,14,18 reterms ,whereas , Desai et al 18 had increased levels of TSH in preterm rather than in term newborns whereas, Gupta 7 , Kim 9 and Armanian 12 did not find any influence of gestational age on it.In our study and in Gupta 7 , Kim 9 , Armanian 12 , Feleke 19 Cord blood TSH was not influenced by birth weight but in Desai et al 18 cord TSH levels fell with increase in weight of newborns.Mode of delivery did not influence Cord blood TSH and T4 levels in our as well as in Fuse et al 5 ,Seth 10 , studies ,while in Herbtsman 20 cesarean section had lower TSH values than vaginal mode of delivery ,Tehrani 21 had higher values of TSH in cesarean group, whereas in Gupta et al 7 , Kim 9 , Armanian 12 and Mehmat et al 22 vaginal mode had higher Cord TSH than cesarean section mode of delivery.Pre ecclampsia had no influence on cord blood TSH in our as well as, Laura et al 23 studies, whereas ,TSH level was more in Pre Ecclampsia group in Kim 12 and ChanY et al 24 and studies.Birth Asphyxia had significant influence on Cord TSH as the levels were increased as compared to normal newborns in our study, Gupta 7 , Kim 9 , Seth 10 and Armanian 12 .H.I.V. status of mother did not influence Cord TSH either in our as well as in Herbtsman study 20 .Thus there were varying results in different studies considering the influence of perinatal factors on thyroid functions in newborns.On follow up of newborns after 7 days, we found two preterm newborns who had raised Serum TSH and low T4, corresponding to their upper and lower limits ,however further follow up and treatment could not be started as free T4 is recommended before starting treatment and the patients were lost to follow up.

Gesta- tional Age TSH 3 rd TSH 97 th TSH 99 th T4 3 rd T4 97 t h T4 99 th
. Studies have been conducted with and its influence of perinatal factors on Cord blood TSH with paradoxical and different results in different studies In our study term newborns had increased levels of cord blood TSH as compared to

Table - 2
:Comparison of Mean TSH & T4 Levels among Preterm ,Term and Post term .Table -3: Effect of Severe Birth Asphyxia on of Mean TSH and T4 Cord blood levels in Preterm, Term and Post term newborns.

Table - 4
: Characteristics of Congenital Hypothyroidism Patients