The association of early pregnancy vitamin D and BMI status with composite adverse pregnancy outcomes: an ancillary analysis of the Vitamin D Antenatal Asthma Reduction Trial.

BACKGROUND

Adverse pregnancy outcomes (APOs) affect ∼20% of pregnancies and pose significant health risks for mothers and fetuses. Identifying risk factors is crucial for developing prevention strategies.

OBJECTIVES

This study examined the association between vitamin D status, measured by 25-hydroxyvitamin D (25(OH)D) concentrations, and APO risk, and whether this association varies by pregnancy timing and body mass index (BMI) (kg/m).

METHODS

In this ancillary analysis of the Vitamin D Antenatal Asthma Reduction Trial, we used multivariable logistic regression models to examine the association between 25(OH)D concentrations in early (10-18 wk) and late (32-38 wk) pregnancy, and development of a composite APO outcome, including pre-eclampsia, gestational hypertension, gestational diabetes, intrauterine growth restriction, and preterm birth.

RESULTS

Among 816 participants in the intention-to-treat analysis, 283 composite APO events occurred. Vitamin D supplementation did not significantly reduce APO risk. Participants who developed APOs had lower baseline 25(OH)D concentrations than those who did not (mean ± SD: 21.72 ± 10.04 vs. 23.47 ± 10.29 ng/mL; mean difference ± SE: 1.75 ± 0.78; P = 0.026). A significant interaction was observed between baseline 25(OH)D and BMI (interaction term, odds ratio [OR]: 1.04; 95% confidence interval [95% CI]: 1.00, 1.08; P = 0.041). Among participants with BMI < 25 (reference group), each unit increase in baseline 25(OH)D (ng/mL) was associated with 4% lower odds of developing an APO (OR: 0.96; 95% CI: 0.93, 0.99; P = 0.013), whereas no association was observed among participants with BMI ≥ 25 kg/m (OR: 1.00; 95% CI: 0.98, 1.02; P = 0.83). Third-trimester 25(OH)D concentrations did not differ between participants with and without APOs.

CONCLUSIONS

Although vitamin D supplementation did not reduce APO risk, higher early pregnancy 25(OH)D concentrations were associated with lower odds of APOs in participants with BMI < 25. These findings highlight the potential importance of higher early pregnancy 25(OH)D concentrations, particularly among those with normal BMI, in reducing APO risk.

TRIAL REGISTRATION

This study is an ancillary analysis from VDAART, which is registered with ClinicalTrials.gov (NCT00920621: https://clinicaltrials.gov/study/NCT00920621?term=vdaart&rank=1).