The relationship between iron level and thyroid function during the first trimester of pregnancy: A cross-sectional study in Wuxi, China

Our objective was to evaluate the relationship between iron level and thyroid function during the first trimester of pregnancy in Eastern China. This was a hospital-based, cross-sectional observational study. A total of 1764 pregnant women were enrolled during their first trimester of gestation in Wuxi city. Serum ferritin (SF), hemoglobin (Hb), urinary iodine concentrations (UIC), thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3) were measured and evaluated in pregnant women. The median of TSH,FT4 and FT3 were 1.53 mIU/L,10.43 pmol/L and 4.50 pmol/L respectively. The median UIC was 200 μg/L and the median Hb was 126 g/L. Of all the women, 1.76% of the subjects had iron deficiency anaemia (IDA) (SF < 20 μg/L and Hb < 105 g/L), and 39.06% of the population had iron deficiency (ID) (SF < 15 μg/L). Compared with SF > 100 μg/L group, the FT4 level was significantly lower in SF < 20 μg/L group (P = 0.031) and in SF 20-100 μg/L group (P = 0.048). The TSH value of SF > 20 μg/L group was significantly higher than that in SF 20-100 μg/L group (P = 0.038) and SF > 100 μg/L group(P = 0.034). There was an inverse linear relationship between TSH and FT4 after log transformation (r = 0.245,P = 0.000). Moreover, spearman's correlation analysis showed that UIC were correlated with SF and FT3 (all P < 0.001) and iodine status more than adequate was associated with reduced serum ferritin concentration and FT3 levels. Thus, it is recommended that iron deficiency and iron deficiency anaemia shoud be evaluated and treated to combat thyroid dysfunction during the first trimester of pregnancy, Meanwhile, an increased attention should be paid on iodine nutritional status among this pregnant women simultaneous iron deficiency and thyroid dysfunction.