Objective To investigate the expression and significance of 25-hydroxyvitamin D 25(OH)D, immune cell subsets, and helper T cell (Th)1 and Th2 in patients with unexplained recurrent spontaneous abortion (URSA).

Methods A total of 307 URSA patients were enrolled as URSA group, which was further divided into non-maintenance of pregnancy group (n=127) and maintenance of pregnancy group (n=180) based on pregnancy maintenance status. Another 307 healthy pregnant women in the same period were selected as control group. The levels of 25(OH)D, immune cell subsets, and Th1/Th2 expression were compared among these groups. Pearson correlation analysis was used to explore the correlations of 25(OH)D and immune cell subsets with Th1/Th2 expression in URSA patients.

Results Compared with the control group, the URSA group had significantly lower levels of 25(OH)D and interleukin-10 (IL-10), and higher levels of CD3⁺, CD3⁺CD4⁺, CD3⁺CD8⁺, CD4⁺/CD8⁺, CD16⁺CD56⁺, CD19⁺, interleukin-2 (IL-2), and tumor necrosis factor-α (TNF-α) (P < 0.001). Compared with the maintenance of pregnancy group, the non-maintenance of pregnancy group had significantly lower levels of 25(OH)D and IL-10, and higher levels of CD3⁺, CD3⁺CD4⁺, CD3⁺CD8⁺, CD4⁺/CD8⁺, CD16⁺CD56⁺, CD19⁺, IL-2, and TNF-α (P < 0.001). Pearson analysis revealed that 25(OH)D in URSA patients was significantly negatively correlated with IL-2 and TNF-α (P < 0.05), while positively correlated with IL-10 (P < 0.05). Immune cell subsets, including CD3⁺, CD3⁺CD4⁺, CD3⁺CD8⁺, CD4⁺/CD8⁺, CD16⁺CD56⁺, and CD19⁺ were significantly positively correlated with IL-2 and TNF-α (P < 0.05), while negatively correlated with IL-10 in URSA patients (P < 0.05).

Conclusion There are abnormalities in 25(OH)D, immune cell subsets, and Th1/Th2 cytokine expression in URSA patients, and these expressions differ in URSA patients with different pregnancy outcomes. The underlying mechanism may be related to the regulation of Th1/Th2 cytokine balance.