ESPE Abstracts

Background: Normal function of the thyroid gland is essential for adequate neurological development of the fetus and child. In previous studies, associations between reduced birth weight and overt maternal and fetal thyroid dysfunction have been described. We hypothesize that also variations within the normal range of fetal thyroid function have an impact on fetal and neonatal growth.

Objective: The aim of this study is to investigate whether thyroid hormones measured at birth are associated with fetal and infant growth in healthy children.

Method: Thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4), and free thyroxine (FT4) were measured in umbilical cord blood samples from the Copenhagen Baby Heart cohort, and in venous blood samples of neonates taken two hours and two months after delivery (the COMPARE cohort). Measurements of head circumference (HC), birth weight (BW) and length (BL) were extracted from medical records. Measurement of HC was repeated two months after birth on children in the COMPARE-cohort and ΔHC as growth in mm/day was calculated. Statistical analyses were performed as Pearson correlations (SAS). This cohort study was initiated in June 2017 and it is expected to be finalized by December 2018. The preliminary analysis is based on the first 2316 cord blood samples, 107 2-hr samples and 83 2-mth samples.

Results: The 2-hr blood samples were collected 2h34m after birth (range 0h28m–5h25m). TSH increased from a cord blood median of 9.3 mU/l (2.4–67.7) to 42.4 mU/l (3.3–125.0), T3 from 1.0 nmol/l (0.2–2.5) to 3.6 nmol/l (1.6–7.2), T4 from 146.0 nmol/l (41.0–252.0) to 214.0 nmol/l (123.0–318.0) and FT4 from 13.9 pmol/l (8.4–21.4) to 21.6 pmol/l (14.2–38.3). Associations between thyroid hormones and anthropometry are shown in Table 1.

Conclusion: Thyroid hormone levels increase considerably from cord blood to 2 hours post partum, likely reflecting delivery-associated stress. We found associations between thyroid hormones and body size including HC at birth, BW, BL as well as body growth from birth to 2 months. This supports the hypothesis that thyroid hormones are involved in general growth and brain development in healthy children.