Characteristics of the subjects
In total, the mean age (±SD) was 29±6 years old, and the mean gestation age (±SD) was 20±4 weeks (550 cases). In this study, the median SF level was 35.63 μg/L (range, 7.14 - 253.49 μg/L), the median Hb level was 115.00 g/L (range, 91.78 - 133.00 g/L), the median T3 level was 2.36 nmol/L (range, 1.43 - 4.14 nmol/L), the median FT3 level was 4.25 pmol/L (range, 2.94 - 6.31 pmol/L), the median T4 level was 110.80nmol/L (range, 64.41 - 181.50 nmol/L), the median FT4 level was 13.49 pmol/L (range, 8.66 - 20.66 pmol/L), and the median TSH level was 1.42 μIU/ml (range, 0.01 - 5.28 μIU/ml), as shown inTable 1 . The ID group was significantly lower in FT3 and FT4, whereas it was significantly higher in TSH (all P < 0.01). The results of the difference analysis of thyroid hormone levels between the two groups of the 550 cases are listed in Table 1 andFigure S1.