A vitamin D signal for pre-eclampsia prevention — but the evidence is thin

Design

Systematic review and network meta-analysis of 8 randomised trials

Population

4,078 high-risk pregnant women

Primary outcome

Incidence of pre-eclampsia

Effect

Vitamin D 4,000 IU/day RR 0.21 (0.06–0.72); 60,000 IU monthly RR 0.36 (0.19–0.70); low certainty

A network meta-analysis of eight randomised trials in 4,078 high-risk pregnant women compared statins, metformin and vitamin D against placebo for pre-eclampsia prevention. Higher-dose vitamin D was associated with fewer cases, with large relative reductions at 4,000 IU/day and 60,000 IU monthly. Statins and metformin gave inconsistent results with wide intervals.

The authors are unusually explicit about the limits: the networks are sparse and partly indirect, certainty is low, and they describe the findings as hypothesis-generating and not intended to guide practice. The large risk ratios are therefore unstable.

So nothing changes at the bedside. Low-dose aspirin from the first trimester remains the evidence-based prophylaxis for women at high pre-eclampsia risk, with calcium where dietary intake is low. This trial is a reason to design better studies of vitamin D, not to start prescribing it at high dose for prevention.

• Across 8 randomised trials (4,078 high-risk women), higher-dose vitamin D was associated with fewer pre-eclampsia cases — 4,000 IU/day risk ratio 0.21 (95% CI 0.06–0.72), 60,000 IU monthly 0.36 (0.19–0.70).
• Evidence for statins and metformin was inconsistent, with wide confidence intervals.
• The authors rate certainty as low and call the findings hypothesis-generating, not a basis for practice.
• Continue low-dose aspirin from the first trimester for women at high pre-eclampsia risk; this analysis does not displace it.

Why it matters

It reopens whether statins, metformin or vitamin D add anything to pre-eclampsia prevention — and the honest answer is that the question is still open.

Don't overread it

These were sparse, indirect comparisons — the large risk reductions are unstable and should not prompt high-dose vitamin D for prevention.

The statistics, in plain English

In a network meta-analysis, treatments not directly compared are linked indirectly through placebo. When few trials feed that network, the estimates are fragile — a risk ratio of 0.21 looks dramatic but its wide interval and low certainty mean it could be much smaller or absent.

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