<p>Comparison across Vitamin D thresholds.</p>

Serum 25(OH)D was quantified. Vitamin D status was categorised as suboptimal (<50 nmol/L) or sufficient (≥50 nmol/L) status. The association between vitamin D status and preeclampsia was assessed using conditional logistic regression.

Odds ratios (ORs) with 95% confidence intervals (CIs) were presented.</p> <p>Results</p><p>Median serum 25(OH)D was significantly lower in preeclampsia cases compared with controls [67.1 nmol/L (interquartile range 47.8–84.0) vs. 77.6 nmol/L (62.4–99.7); <i>P</i> = 0.001]. Suboptimal vitamin D levels (<50 nmol/L) were observed in 32.2% of preeclampsia cases versus 6.8% of controls (<i>P</i> = 0.002). In conditional logistic regression accounting for matching, women with suboptimal vitamin D had higher odds of preeclampsia (OR 8.0; 95% CI: 1.84–34.78; <i>P</i> = 0.006).

Each 10 nmol/L decrease in serum 25(OH)D was associated with a 29% increase in preeclampsia odds (OR 1.29; 95% CI: 1.09–1.54; <i>P</i> = 0.004).</p> <p>Conclusions</p><p>In this study, suboptimal maternal serum vitamin D status demonstrated a significant association with preeclampsia. There is potential value in antenatal screening for vitamin D status. Findings support further research into vitamin D supplementation as a preventive intervention for preeclampsia.</p> <p>Trial registration</p><p>Pan African Clinical Trial Registry (<a href="clinicaltrials.gov/ct2/show/PACTR202505516303679" target="_blank">PACTR202505516303679</a>).</p></div>