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Preterm to term infant postmenstrual age reference intervals for thyroid-stimulating hormone and free thyroxine



Infants born preterm are affected by a hypothalamic−pituitary−thyroid axis that is immature and still developing as they progress closer to corrected term gestation. Multiple risk factors place preterm infants at risk for a hypothyroid state. However, there is variability in thyroid-stimulating hormone cutoff values and limited data on free thyroxine reference intervals to guide clinicians.


1584 thyroid-stimulating hormone and 1576 free thyroxine laboratory samples that were originally collected to screen hospitalized infants for delayed-onset of hypothyroidism were retrospectively evaluated from a group of 1087 infants who ranged in postmenstrual age from 25 to 43 weeks gestation at the time of laboratory sample collection. Median thyroid hormone values and reference intervals were established using R and the mixtools package.


Thyroid-stimulating hormone reference intervals remained similar across gestational ages from 0.340–9.681 µIU/mL in 25–27 6/7-week infants to 1.090–7.627 µIU/mL in 40–43-weeks infants. For the same age groups, free thyroxine reference intervals increased from 0.42–0.91 ng/dL to 0.87–1.32 ng/dL.


The reference intervals identified suggest that infants <31 weeks gestation have a higher thyroid-stimulating hormone and lower free thyroxine level at baseline than previously anticipated.


  • The increasing free thyroxine values in preterm to term infants indicate a maturing hypothalamic−pituitary−thyroid axis. Clinicians need thyroid hormone reference intervals that also vary by postmenstrual age to aid the evaluation of sick preterm infants who are at risk of a delayed hypothyroidism diagnosis that can be missed on the initial newborn screen.

  • This study provides one of the largest samples of thyroid-stimulating hormone and free thyroxine data to establish reference intervals in preterm infants.

  • Clinicians may utilize the identified postmenstrual age-based reference intervals to inform follow-up thyroid testing in preterm infants at several weeks postnatal age.

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Fig. 1: Flowchart of Study Participants.
Fig. 2: TSH Values According to Postmenstrual Age.
Fig. 3: TSH median laboratory values with reference intervals organized by postmenstrual age groupings.
Fig. 4: FT4 Values According to Postmenstrual Age.
Fig. 5: Median FT4 According to Postmenstrual Age Subgroups.


  1. LaFranchi, S. H. Newborn screening strategies for congenital hypothyroidism: an update. J. Inherit. Metab. Dis. 33, S225–S233 (2010).

    Article  Google Scholar 

  2. Vigone, M. C. et al. Evolution of thyroid function in preterm infants detected by screening for congenital hypothyroidism. J. Pediatr. 164, 1296–1302 (2014).

    CAS  Article  Google Scholar 

  3. Woo, H. C. et al. Congenital hypothyroidism with a delayed thyroid-stimulating hormone elevation in very premature infants: incidence and growth and developmental outcomes. J. Pediatr. 158, 538–542 (2011).

    CAS  Article  Google Scholar 

  4. Corbetta, C. et al. A 7-year experience with low blood TSH cutoff levels for neonatal screening reveals an unsuspected frequency of congenital hypothyroidism (CH). Clin. Endocrinol. 71, 739–745 (2009).

    CAS  Article  Google Scholar 

  5. Sun, X. et al. Free thyroxine and thyroid-stimulating hormone reference intervals in very low birth weight infants at 3-6 weeks of life with the Beckman Coulter Unicel Dxl 800. Clin. Biochem. 47, 16–18 (2014).

    CAS  Article  Google Scholar 

  6. Larson, C., Hermos, R., Delaney, A., Daley, D. & Mitchell, M. Risk factors associated with delayed thyrotropin elevations in congenital hypothyroidism. J. Pediatr. 143, 587–591 (2003).

    CAS  Article  Google Scholar 

  7. American Academy of Pediatrics, et al. Update of newborn screening and therapy for congenital hypothyroidism. Pediatrics 117, 2290–2303 (2006).

    Article  Google Scholar 

  8. Kilberg, M. J., Rasooly, I. R., LaFranchi, S. H., Bauer, A. J. & Hawkes, C. P. Newborn screening in the US may miss mild persistent hypothyroidism. J. Pediatr. 192, 204–208 (2018).

    Article  Google Scholar 

  9. Williams, F. & Hume, R. The measurement, definition, aetiology and clinical consequences of neonatal transient hypothyroxinaemia. Ann. Clin. Biochem. 48, 7–22 (2011).

    CAS  Article  Google Scholar 

  10. Leger, J. et al. European Society for Paediatric Endocrinology consensus guidelines on screening, diagnosis, and management of congenital hypothyroidism. J. Clin. Endocrinol. Metab. 99, 363–384 (2014).

    CAS  Article  Google Scholar 

  11. Wang, Y. et al. Establishment of reference intervals for thyroid hormones in premature infants beyond the first week of life using Beckman Coulter Unicel DxI 800. Clin. Biochem. 74, 19–23 (2019).

    CAS  Article  Google Scholar 

  12. Chaudhari, M. & Slaughter, J. L. Thyroid function in the neonatal intensive care unit. Clin. Perinatol. 45, 19–30 (2017).

    Article  Google Scholar 

  13. Kaluarachchi, D. C., Allen, D. B., Eickhoff, J. C., Dawe, S. J. & Baker, M. W. Thyroid-stimulating hormone reference ranges for preterm infants. Pediatrics 144, e20190290 (2019).

    Article  Google Scholar 

  14. Grob, F. & Van Vliet, G. Avoiding the overdiagnosis of congenital hypothyroidism in premature newborns. Pediatrics 144, e20191706 (2019).

    Article  Google Scholar 

  15. Bijarnia, S., Wilcken, B. & Wiley, V. C. Newborn screening for congenital hypothyroidism in very-low-birth-weight babies: the need for a second test. J. Inherit. Metab. Dis. 34, 827–833 (2011).

    Article  Google Scholar 

  16. McGrath, N., Hawkes, C. P., Mayne, P. & Murphy, N. P. Optimal timing of repeat newborn screening for congenital hypothyroidism in preterm infants to detect delayed thyroid-stimulating hormone elevation. J. Pediatr. 205, 77–82 (2019).

    CAS  Article  Google Scholar 

  17. Delahunty, C. et al. Levels of neonatal thyroid hormone in preterm infants and neurodevelopmental outcome at 5 ½ years: millennium cohort study. J. Clin. Endocrinol. Metab. 95, 4898–4908 (2010).

    CAS  Article  Google Scholar 

  18. Reuss, M. L., Paneth, N., Pinto-Martin, J. A., Lorenz, J. M. & Susser, M. The relation of transient hypothyroxinemia in preterm infants to neurologic development at two years of age. N. Engl. J. Med. 334, 821–827 (1996).

    CAS  Article  Google Scholar 

  19. Williams, F. L. & Hume, R. Perinatal factors affecting thyroid hormone status in extreme preterm infants. Semin. Perinatol. 32, 398–402 (2008).

    Article  Google Scholar 

  20. Engle, W. A. & American Academy of Pediatrics Committee on Fetus and Newborn. Age terminology during the perinatal period. Pediatrics 114, 1362–1364 (2004).

  21. Ohio Department of Health. NBS Guidelines for NICU and Special Care Infants [internet]. (2018).

  22. Pruim, R., Kaplan, D. T. & Horton, N. J. The mosaic Package: helping students to think with data using R. R. J. 9, 77–102 (2017).

    Article  Google Scholar 

  23. Bengalia, T. & Chauveau, D. mixtools: an R package for analyzing finite mixture models. J. Stat. Softw. 32, 1–29 (2009).

    Google Scholar 

  24. R.C. Team. R: a language and environment for statistical computing. R version 4.0.2 (2020-06-22)—“Taking Off Again”. (2020).

  25. Peterson, R. A. & Cavanaugh, J. E. Ordered quantile normalization: a semiparametric transformation built for the cross-validation era. J. Appl. Stat. 47, 1–16 (2019).

    Google Scholar 

  26. Tukey, J. Exploratory Data Analysis 1st edn (Pearson, 1977).

  27. Holmes, D. T. & Buhr, K. A. Widespread incorrect implementation of the Hoffman method, the correct approach, and modern alternatives. Am. J. Clin. Pathol. 151, 328–336 (2018).

    Article  Google Scholar 

  28. Murphy, N. et al. The hypothalamic-pituitary-thyroid axis in preterm infants; changes in the first 24h of postnatal life. J. Clin. Endocrinol. Metab. 89, 2824–2831 (2004).

    CAS  Article  Google Scholar 

  29. Thorpe-Beeston, J. G., Nicolaides, K. H., Felton, C. V., Butler, J. & McGregor, A. M. Maturation of the secretion of thyroid hormone and thyroid-stimulating hormone in the fetus. N. Engl. J. Med. 324, 532–536 (1991).

    CAS  Article  Google Scholar 

  30. Aktas, O. N., Gursoy, T., Soysal, E., Esencan, E. & Ercin, S. Thyroid hormone levels in late preterm, early term and term infants: a study with healthy neonates revealing reference values and factors affecting thyroid hormones. J. Pediatr. Endocrinol. Metab. 30, 1191–1196 (2017).

    CAS  Article  Google Scholar 

  31. Wong, J. S. L. et al. Reference intervals for thyroid-stimulating hormone (TSH) and free thyroxine (FT4) in infants’ day 14-30 of life and a comparison with other studies. J. Pediatr. Endocrinol. Metab. 33, 1125–1132 (2020).

    CAS  Article  Google Scholar 

  32. CLSI. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline—Third Edition. CLSI document EP28-A3c (Clinical and Laboratory Standards Institute, 2008).

  33. Glass, H. C. et al. Outcomes for extremely premature infants. Anesth. Analg. 120, 1337–1351 (2015).

    Article  Google Scholar 

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All authors made substantial contributions to the conception and design, acquisition of data, or analysis and interpretation of data. All authors contributed towards drafting the article or revising it critically for important intellectual content. All authors gave final approval of the version to be published.

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Correspondence to Jonathan L. Slaughter.

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For this cohort study using laboratory values that were previously collected in a neonatal intensive care unit per local standard of care, the Nationwide Children’s Hospital Institutional Review Board deemed this research to be no more than minimal risk and granted a waiver of informed consent.

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Ziegler, G.M., Slaughter, J.L., Chaudhari, M. et al. Preterm to term infant postmenstrual age reference intervals for thyroid-stimulating hormone and free thyroxine. Pediatr Res 91, 1130–1135 (2022).

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