Myo-inositol and Gestational Diabetes: The Science vs the Hype in 2026

The best available answer is split down the middle: a 2023 Cochrane review of 6 trials in 1,140 pregnant women found myo-inositol may reduce gestational diabetes by 47% (RR 0.53, 95% CI 0.31 to 0.90) at low to very low certainty (PMID 36790138), and then the largest placebo-controlled trial ever run, 464 pregnant women with PCOS at 13 Dutch hospitals, found no reduction at all, 25.0% versus 26.8% for the composite of gestational diabetes, preeclampsia or preterm birth (RR 0.93, 95% CI 0.68 to 1.28) (PMID 40920401). This is a claim autopsy: how a 47% headline was built, and why the market has not revised it. The whole evidence profile is on the myo-inositol review hub.

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How the 47% was built

The Cochrane update searched to March 2022 and pooled 7 randomized trials of antenatal myo-inositol in 1,319 women at 10 to 24 weeks of gestation without pre-existing diabetes. Six of the seven trials were Italian and one was Irish. Myo-inositol was associated with fewer cases of gestational diabetes (RR 0.53, 6 studies, 1,140 women) and fewer hypertensive disorders of pregnancy (RR 0.34, 95% CI 0.19 to 0.61), with no clear effect on gestational weight gain (-0.25 kg, 95% CI -1.26 to 0.75) or caesarean section (RR 0.91, 95% CI 0.77 to 1.07) (PMID 36790138). The reviewers rated the certainty low to very low, which is the technical way of saying that the true effect could be substantially different from the estimate. They also flagged a possible signal of neonatal hypoglycaemia, RR 3.07 with an interval from 0.90 to 10.52, and no data on perinatal mortality.

The trial that should have changed the conversation

The Dutch trial enrolled 464 pregnant individuals with PCOS at 8 to 16 weeks of gestation between June 2019 and March 2023, randomized them to myo-inositol 2 g with 0.2 mg folic acid twice daily (n=230) or placebo with folic acid (n=234) until delivery, and followed a prespecified composite of gestational diabetes, preeclampsia or preterm birth before 37 weeks. The primary outcome occurred in 56 of 230 women on myo-inositol and 61 of 234 on placebo, an absolute difference of about 1.8 percentage points and a relative risk of 0.93 (P = 0.67) (PMID 40920401). It is double-blind, placebo-controlled, multicenter and larger than any single trial in the Cochrane pool. Two caveats apply: baseline hyperandrogenism was imbalanced between arms (29.0% versus 18.5%), and the population was 86.1% White and limited to women with PCOS, who carry a higher baseline risk of gestational diabetes than the general pregnant population the Italian trials enrolled.

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The chain of hype here runs from paper to prenatal label. The Cochrane estimate became “47% lower risk of gestational diabetes” on supplement packaging and in fertility clinic handouts. The Dutch result arrived in 2025 and the marketing did not move. Under the HYPE Index this is the E5 failure, update behavior after contradicting evidence, and it is why the claim scores 49 despite a Cochrane review in its favor.

What we do not know

Whether the Italian results generalize beyond the centers that produced them; whether the null Dutch result applies to pregnancies without PCOS; whether the neonatal hypoglycaemia signal is real; and anything about perinatal mortality, which no trial in the Cochrane pool reported (PMID 36790138). A 26-study narrative review of inositol in diabetes and gestational diabetes concluded that larger and longer trials were needed before inositol could be considered an effective management strategy, and gave no pooled effect sizes (PMID 29053004). The Dutch trial did not state its funding in the abstract.

Doses used in studies

These are doses reported by the named sources, not recommendations.

Back to the myo-inositol review hub, or read what the trials reported on myo-inositol side effects. HDAI’s overview of nutrition and metabolic health covers the dietary side of blood sugar in pregnancy and beyond.

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