Correlation analysis between serum 25-hydroxyvitamin D levels and thyroid peroxidase antibody positivity in preconception women.

BACKGROUND

Vitamin D insufficiency and TPOAb positivity frequently coexist in women planning pregnancy, yet their joint distribution and clinical correlates immediately before conception remain insufficiently characterized in routine preconception practice.

OBJECTIVE

This retrospective study aimed to examine the association between serum 25(OH)D concentrations and TPOAb positivity in preconception women, to assess whether low vitamin D status and TPOAb positivity were jointly associated with lower pregnancy rates, and to explore the robustness of these associations after adjustment for demographic, thyroid-related, reproductive, seasonal, and nutritional covariates.

METHODS

A total of 256 preconception women who underwent routine preconception evaluation in the Department of Premarital and Preconception Health Care between January 2021 and December 2023 were retrospectively enrolled. Serum 25(OH)D, TPOAb, TgAb, thyroid-stimulating hormone, free thyroxine, anti-Müllerian hormone, ferritin, fasting blood glucose, urinary iodine concentration, and season of blood sampling were recorded from existing clinical records. TPOAb reference range was 0-9 IU/mL; for the primary analysis, TPOAb positivity was prespecified as ≥ 34 IU/mL. Multivariable logistic regression and interaction analyses were used to evaluate factors associated with TPOAb positivity and retrospectively ascertained 12-month pregnancy outcomes.

RESULTS

Among 256 participants (mean age 30.2 ± 4.1 years), 67 women (26.2%) were classified as TPOAb-positive. The TPOAb-positive group had lower serum 25(OH)D levels than the TPOAb-negative group (24.8 ± 9.6 vs. 31.4 ± 11.2 ng/mL, P = 0.003), and serum 25(OH)D was inversely correlated with TPOAb concentration (r = -0.287, P = 0.008). After adjustment for age, BMI, TSH, FT4, AMH, season, urinary iodine category, ferritin, and recent vitamin D intake, vitamin D deficiency remained independently associated with TPOAb positivity (adjusted OR 2.21, 95% CI 1.09-4.48, P = 0.028). In 218 women with follow-up, the 12-month pregnancy rate was 42.7% overall; women with concomitant TPOAb positivity and vitamin D deficiency/insufficiency had the lowest rate (28.6%), and the TPOAb-by-vitamin D interaction for pregnancy outcome was adverse (Pinteraction = 0.041).

CONCLUSIONS

Lower serum 25(OH)D levels were independently associated with TPOAb positivity in preconception women. The coexistence of low vitamin D status and TPOAb positivity was associated with less favorable short-term pregnancy outcomes, although the observational design does not support causal inference.

CLINICAL TRIAL NUMBER: Not applicable.