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Dynamic Change of Thyroid Hormones With Postmenstrual Age in Very Preterm Infants Born With Gestational Age <32
Ranran Shi1,2, Ming Zhang1,2, Yao Chen1,2
1Department of Neonatology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, China.
Insights
Thyroid hormone reference ranges for very preterm infants (VPIs) are established, showing distinct changes with postmenstrual age (PMA). Age-related cutoffs are recommended over single ranges for diagnosing congenital hypothyroidism in VPIs.
Area of Science:
- Neonatal endocrinology
- Pediatric thyroid disorders
- Congenital hypothyroidism screening
Background:
- Thyrotropin (TSH) and free thyroxine (FT4) relationships with postmenstrual age (PMA) in preterm infants are unclear.
- Lack of standard thyroid hormone reference ranges leads to varied diagnostic criteria for congenital hypothyroidism.
Purpose of the Study:
- Investigate TSH/FT4 and PMA relationship in very preterm infants (VPIs) (GA <32 weeks).
- Derive thyroid function reference charts based on PMA for VPIs.
Main Methods:
- Prospective cohort study of 1,093 VPIs (GA <32 weeks).
- Serial TSH and FT4 measurements weekly in the first month, and at PMA 36, 40 weeks, and discharge.
- Calculated 2.5th, 5th, 50th, 95th, and 97.5th percentiles to create PMA-based charts.
Main Results:
- TSH and FT4 percentile charts based on PMA were generated.
- TSH peaked at PMA 30 weeks, then decreased, reaching full-term levels by PMA 38-40 weeks.
- FT4 reached lowest point at PMA 26-27 weeks, then increased, reaching full-term levels by PMA 38-40 weeks.
Conclusions:
- TSH and FT4 in VPIs exhibit characteristic changes with PMA.
- Age-related cutoffs are more suitable than single reference ranges for VPIs.
- Repeated thyroid function screening is essential for preterm infants.
Background:
At present, the relationship between thyrotropin (TSH) and free thyroxine (FT4) in relation to postmenstrual age (PMA) in preterm infants is still unclear, and there is no reliable standard thyroid hormone reference ranges, resulting in different diagnostic criteria for congenital hypothyroidism been used by different newborn screening programs and different countries.
Objectives:
To investigate the relationship between TSH/FT4 and PMA in very preterm infants (VPIs) born with gestational age (GA) <32 weeks and to derive thyroid function reference charts based on PMA.
Methods:
A prospective cohort study was performed on VPIs born with GA<32 weeks and born in or transferred to the 27 neonatal intensive care units from January 1, 2019 to December 31, 2019. Serial TSH and FT4 values were measured at the end of each week during the first month after birth and also at PMA36 weeks, PMA40 weeks and at discharge, respectively. The 2.5th, 5th, 50th, 95th, and 97.5th percentiles of TSH and FT4 of different PMA groups were calculated to draw the percentile charts based on PMA.
Results:
1,093 preterm infants were included in this study. The percentile charts of TSH and FT4 levels based on PMA were drawn respectively, and the result indicated that the percentile charts of TSH values were gradually increased initially and then decreased with increasing PMA. The 97.5th percentile chart reached the peak at PMA30 weeks (17.38μIU/ml), and then decreased gradually, reaching the same level as full-term infants (9.07μIU/ml) at PMA38-40 weeks. The 2.5th percentile chart of FT4 was at its lowest point at PMA26-27 weeks (5.23pmol/L), then increased slowly with PMA and reached the same level as full-term infants at PMA38-40 weeks (10.87pmol/L). At PMA36 weeks, the reference intervals of the 2.5th to 97.5th percentiles of TSH and FT4 were 1.18-12.3μIU/ml and 8.59-25.98pmol/L, respectively.
Conclusion:
The percentile charts of TSH and FT4 in VPIs showed characteristic change with PMA. The results prompt that age-related cutoffs, instead of a single reference range, might be more useful to explain the thyroid function of VPIs. And repeated screening is necessary for preterm infants.
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