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The problem
Intervention: Vitamin D supplementation versus placebo
Who it was tested with: Pregnant women with gestational diabetes mellitus (1,737 patients across 20 studies).
Experience from people who deliver programmes: stories, case studies and lessons learned. Valuable for understanding how and why, and for spotting what to test next, but not a measure of effect.
"Twenty studies involving 1,737 patients were included. Meta-analysis showed that compared to placebo, vitamin D supplementation significantly reduced fasting glucose (SMD: -1.01, p = 0.0002), 2-h postprandial glucose (SMD: -0.89, p = 0.0002)... and was associated with lower incidences of cesarean delivery (RR: 0.68, p < 0.0001)... preterm birth (RR: 0.28, p < 0.0001)." This pooled analysis of multiple randomized trials provides experimental-level evidence comparing vitamin D to placebo in a defined population.
Substantial heterogeneity among included studies and methodological limitations in individual trials reduce confidence in the findings. No information on optimal dosage, timing, or safety profiles. Publication bias not fully assessed.
Across countries and designs
4 studies · 3 countries
