Research Summary

No Benefit of Myo-Inositol for Preventing Gestational Diabetes, Preeclampsia, or Preterm Birth in PCOS

Kate Young

Key Highlights

  • Daily myo-inositol supplementation in pregnancy did not reduce the incidence of gestational diabetes, preeclampsia, or preterm birth in individuals with polycystic ovary syndrome (PCOS).
  • The primary composite outcome occurred in 25.0% of participants in the myo-inositol group versus 26.8% in the placebo group.
  • No significant maternal or neonatal benefits were observed, except for a lower rate of planned cesarean delivery in the myo-inositol group.
  • Findings do not support recommending antenatal myo-inositol supplementation for patients with PCOS.

Pregnant individuals with polycystic ovary syndrome (PCOS) are at increased risk of gestational diabetes, preeclampsia, and preterm birth. This trial investigated whether myo-inositol supplementation could reduce these complications, given prior evidence of metabolic benefits in PCOS and earlier, smaller studies suggesting improved pregnancy outcomes in other high-risk groups.

The multicenter, double-blind, placebo-controlled MYPP trial enrolled 464 pregnant participants with PCOS from 13 hospitals in the Netherlands between 2019 and 2023. Participants were randomized to receive either myo-inositol (4 g daily plus 0.4 mg folic acid) or placebo (0.4 mg folic acid) from 8–16 weeks’ gestation until delivery. The primary outcome was a composite of gestational diabetes, preeclampsia, or preterm birth.

The composite outcome occurred in 25.0% of the myo-inositol group and 26.8% of the placebo group, a nonsignificant difference (RR, 0.93; 95% CI, 0.68–1.28; P = .67). Secondary outcomes, including individual components of the composite outcome, other maternal complications, and neonatal outcomes, did not differ significantly between groups. Adherence was modest, with only 38.9% of participants in the intervention group achieving ≥80% compliance. A lower rate of planned cesarean delivery was observed in the intervention arm (5.9% vs 11.6%; RR, 0.51; 95% CI, 0.27–0.97; P = .04), though overall cesarean rates were not reduced.

Study limitations include a higher baseline prevalence of biochemical hyperandrogenism in the myo-inositol group, a lower-than-expected incidence of the primary outcome, and suboptimal supplement adherence. These factors may have influenced effect size detection, though the small absolute between-group difference suggests true lack of benefit.

“Supplementation with myo-inositol at a dose of 4 g per day is not associated with improved pregnancy outcomes and should not be recommended as dietary advice for pregnant individuals with PCOS,” the study authors concluded.

Reference:
van der Wel AWT, Frank CMC, Bout-Rebel R, et al. Myo-inositol supplementation to prevent pregnancy complications in polycystic ovary syndrome: a randomized clinical trial. JAMA. Published online September 8, 2025. doi:10.1001/jama.2025.13668