Daily myo-inositol supplementation during pregnancy might not reduce the risk for major complications for individuals with polycystic ovary syndrome (PCOS), according to new research. 

Although previous small trials suggested that the supplement could help prevent gestational diabetes in women with PCOS, the randomized trial, published in JAMA, found no reduction in major pregnancy complications in these women. 

The findings suggest clinicians should not recommend the supplement for improving obstetric outcomes, underscoring that established approaches, such as lifestyle interventions, routine screening, and blood pressure monitoring, remain reliable strategies to manage risks. 

“If patients are already taking it and tolerating it, clinicians can advise them that current evidence does not support benefit for obstetric outcomes,” said Anne van der Wel, MD, research associate in obstetrics and gynecology at Amsterdam University Medical Center in Amsterdam, Netherlands, and lead author of the findings. 

van der Wel and her colleagues enrolled 464 pregnant women with PCOS from across 13 hospitals in Netherlands. Participants were randomized to receive either 4 g/d myo-inositol plus folic acid or placebo plus folic acid from 8 to 16 weeks of gestation until time of delivery. 

The primary outcome — a composite of gestational diabetes, preeclampsia, or preterm birth before 37 weeks — occurred in 25.0% of those in the myo-inositol group and 26.8% in the placebo group (relative risk, 0.93; 95% CI, 0.68-1.28; P = .67). The trial was powered to detect a 35% risk reduction, but because fewer complications occurred than expected, it may not have been able to detect a smaller effect. 

In the myo-inositol group vs placebo group, gestational diabetes developed in 17.0% vs 15.8%, preeclampsia occurred in 2.2% vs 4.8%, and preterm birth occurred in 7.6% vs 9.3% of women, respectively. 

Secondary maternal and neonatal outcomes — including gestational hypertension, cesarean delivery rates, neonatal intensive care admissions, and infant birth weights — were similar between groups, with no statistically significant differences. 

The study also found a lower rate of planned cesarean delivery in the myo-inositol group (5.9% vs 11.6%). However, van der Wel cautioned against overinterpreting the result. 

“We believe this to be most likely a chance result,” said van der Wel. “This was a secondary outcome, and the trial was not powered for mode-of-delivery endpoints.” 

Findings from small studies have suggested myo-inositol may help prevent gestational diabetes in at-risk women. 

Lisa Luther, MD, ob/gyn at Massachusetts General Hospital in Boston, who was not involved in the study, said her patients rarely take myo-inositol during pregnancy. She said the findings reinforce a cautious approach to endorsing the supplement. 

“Although some evidence suggests it may increase insulin sensitivity and therefore reduce the incidence of gestational diabetes, the data are not generalizable and are inconsistent,” Luther said. 

Luther said she checks A1c levels during the first prenatal visit for women with PCOS. If results indicate prediabetes, she initiates early gestational diabetes screening at around 24 weeks — earlier than the standard 28-week screening. And she advises patients to start exercise routines prior to conceiving to form habits. 

“There is excellent data that routine exercise and healthy diet during pregnancy can decrease the risk of developing gestational diabetes,” she said. 

van der Wel echoed this advice and said that established preventive measures remain the standard of care. 

“For now, the strongest levers remain preconception optimization of weight and metabolic health, guideline-concordant gestational diabetes screening, blood pressure monitoring, aspirin when otherwise indicated, and targeted lifestyle counseling during pregnancy,” she said. 

van der Wel and Luther disclosed having no conflicts of interest. Various other study authors reported receiving travel and speaker fees, research grants, personal fees from Ferring, Roche Diagnostics, and Merck, among others. The study was funded by a grant from Netherlands Organization for Health Research and Development.

Lara Salahi is a health journalist based in Boston.