Free thyroxine in early pregnancy is an independent negative predictor of 3 rd trimester HbA1c. Odense Child Cohort.

BACKGROUND Lower thyroid function outside pregnancy is associated with increased risk of type 2 diabetes mellitus. The relationship between thyroid function in early pregnancy and glucose status in 3rd trimester has not been investigated. AIMS To study the association between 1st trimester thyroid function and 3rd trimester glucose status. DESIGN In the prospective study Odense Child Cohort (OCC), 1,041 women had 1st trimester blood samples analyzed for thyroid stimulating hormone (TSH), free T4 (FT4), thyroid peroxidase antibody, and HbA1c. Third trimester (week 28) fasting blood samples included plasma glucose, insulin and HbA1c. Oral glucose tolerance test (OGTT, 75 g glucose) was performed in 509 women. First trimester FT4 was dichotomized > vs. ≤ the 25th percentile (25p= 12.9 pmol/L). Homeostatic model assessment - insulin resistance (HOMA)-IR and HOMA-β were calculated RESULTS: Women with FT4 ≤ 25p had significantly higher HbA1c in 1st and 3rd trimesters and higher 3rd trimester fasting glucose, insulin, HOMA-IR and HOMA-β compared to women with FT4 > 25p. In multiple regression analyses, FT4 was an independent negative predictor of 3rd trimester HbA1c. FT4 levels in 3rd and 4th quartiles (high-normal FT4 levels) showed closest inverse associations with HbA1c (P-trend <0.001). TSH was not associated with 3rd trimester HbA1c. CONCLUSION Women with lower levels of FT4 in early pregnancy had higher HbA1c in 3rd trimester and FT4 was an independent negative predictor of 3rd trimester HbA1c.