Fetal and neonatal thyroid function, review and summary of significant new findings.

Thyroid stimulating hormone (TSH) is the hormone most commonly analyzed when an infant is tested for congenital hypothyroidism (CH).  Since tests for CH  are required by state law, data for infant TSH is often available and no additional blood draw is required for  the proposed investigation of the effects of iodine-uptake inhibitor-exposure on infant thyroid hormone (TH) levels.  However, a number of factors need to be considered when correlating exposures with TSH.  Neonatal TSH rises at birth and then subsides to over the next several weeks.   This makes standardization of timing of sample collection important, as failure to do so creates a powerful potential confounder when comparing TSH levels among cohorts or even in determining if an individual infant’s TSH is elevated or in the process of stabilizing.    

There is no national protocol for testing for congenital hypothyroidism, and the best approach is a topic of current debate and investigation.[1]  Texas uses neonatal thyroxine (T4) levels to test newborns for congenital hypothyroidism because these levels are somewhat more stable, peaking at 24 hours after birth,[2] and because the assay is less expensive than that for TSH (Texas Department of Health 2011, Personal Communication).  Texas State Law requires that all infants receive a T4 test at least 24 hours after birth, but before discharge from the hospital.   It is also mandated that all infants receive a second test 1-2 weeks after birth.  Infants whose T4 levels fall in the bottom 10^th centile receive a confirmatory TSH test.[3][MSOffice1]  , which would add additional data and statistical power to the proposed study. 

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[1] Raymond J, LaFranchi SH.  2010.  Fetal and neonatal thyroid function: review and summary of significant new findings.  Current Opinion in Endocrinology, Diabetes and Obesity.  17:1-7.

[2] Brown RS, Huang SA, Fisher D.  2000.  The maturation of thyroid function in the perinatal period and during childhood.  In: Braverman LE, Utiger RD, editors, Werner and Ingbar’s The Thyroid.  Philadelphia, PA.  Lippincott Williams and Wilkins.  pp. 1013-1028.

[3] Texas Department of State Health Services.  2011.  Newborn Screening Case Mangement.  Congenital hypothyroidism: Guidelines for Professionals.  http://www.dshs.state.tx.us/newborn/c_thyro.shtm

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 [MSOffice1]Need to find out if the results are easily linked back to kids with normal ranges.