Statistical analysis
According the concentration of serum ferritin, pregnant women were classified into two groups (ID group and Normal group). Statistical analysis was performed using the Statistical Product and Service Solutions software (SPSS, version 24.0, IBM SPSS Statistics, USA) and the R Programming Language (R, version 4.0.4, Ross Ihaka,Robert Gentleman). Kolmogolov-Smirnov and Shapiro-Wilk tests were used to analyze data distribution normality. All the subjects showed skewed distribution. Thus, each group of statistics were described with medians and percentile values. Then, nonparametric Mann-Whitney U test was used to compare the differences between the two groups. Spearman’s rank correlation test was used to estimate the relationship between serum ferritin and thyroid heroines, hemoglobin, and thyroid heroines separately. The factors of iron nutritional status and thyroid heroines were used to analyze the canonical correlation to extract principal features through the correlation between two sets of variables to further explore the relationship between iron nutritional status and thyroid heroines. Elastic network regression was used to explore their specific relationship. The result was considered as statistically significant difference when the 2-tailed P-value was < 0.05.