Ultrasound Measurements of Thyroid Gland Volume at 36 Weeks' Corrected Gestational Age in Extremely Preterm Infants Born before 28 Weeks' Gestation.

Background: Thyroid ultrasound is a non-invasive imaging tool and provides good evaluation of thyroid anatomy, location, vascularisation, and echogenicity. The aim of this study was to assess thyroid function and thyroid volume in extremely preterm infants born before 28 weeks' gestation evaluated at 36 weeks' corrected gestational age (CGA) compared to term infants' normative data in the literature.

Design: In this largest prospective UK study of extremely premature infants born at less than 28 weeks' gestation, thyroid volume measurement was assessed at 36 weeks' CGA. Fifty-five extremely preterm infants (28 males) who were born before 28 weeks' gestation were recruited to the study. All infants had ultrasound assessment of the thyroid gland at 36 weeks' CGA. We also prospectively measured thyroid stimulating hormone (TSH) and free thyroxine (FT4 ) in all infants at the time of recruitment (within 5 days of birth), at days 14, 21, and 28, and at 36 weeks' CGA.

Results: The mean thyroid volume was measured at 0.57 mL (SD ±0.18). There was no association between mean thyroid volume and thyroid function (TSH or FT4 ). No associations were found between mean thyroid volume and gestation or birth weight in these infants.

Conclusions: Our findings provide a reference range with a mean thyroid volume of 0.57 mL (SD ±0.18) in this extremely preterm age group if less than 28 weeks' gestation. Thyroid volume at birth can vary from country to country due to variations in iodine intake as well as gestational age.