Hypothyroxinemia and weight velocity in preterm infants

Area of Science:

• Neonatal Endocrinology
• Pediatric Growth and Development

Background:

• Hypothyroxinemia of prematurity (HOP) is defined by low free thyroxine (FT4) and normal/low thyroid-stimulating hormone (TSH).
• Understanding FT4 and TSH dynamics is crucial for very preterm infants' growth and development.

Purpose of the Study:

• To establish reference FT4 and TSH values in very preterm infants (<32 weeks postmenstrual age, PMA).
• To investigate the association between HOP, levothyroxine treatment, and growth velocity at 28 days and 36 weeks PMA.

Main Methods:

• Retrospective analysis of 589 preterm neonates (<32 weeks PMA) screened for HOP.
• Measurement of FT4 and TSH levels between postnatal days 4-14.
• Calculation of growth velocity and multivariate regression analysis incorporating PMA, sex, and race.

Main Results:

• Infant's postmenstrual age at birth inversely correlated with FT4 and TSH levels.
• Free thyroxine (FT4) and gestational age were significantly associated with growth velocity at 28 days and 36 weeks PMA.
• Thyroid-stimulating hormone (TSH) levels and levothyroxine treatment did not show a significant association with growth velocity.

Conclusions:

• This study provides a substantial dataset for FT4 and TSH reference ranges in very preterm infants.
• Hypothyroxinemia of prematurity may be a significant factor contributing to impaired postnatal growth in this vulnerable population.