Inositol Dose in Pregnancy for Gestational Diabetes

What clinical trials actually used, when they started, and who they studied.

Key takeaways

• Most prevention trials used myo-inositol 2 g twice daily (4 g/day) starting in the first trimester with folic acid.
• For treatment after GDM diagnosis, cohorts used 4 g/day myo-inositol alongside standard care, improving glycemia and lowering insulin needs.
• Evidence quality is mixed: some meta-analyses find benefit, but a 2023 Cochrane review says evidence is insufficient to confirm prevention of GDM. One 2022 meta-analysis was retracted. Discuss supplements with your clinician.

How inositol has been studied for gestational diabetes

Key points

• Two separate questions: prevention in at-risk pregnancies vs treatment after GDM diagnosis.
• Doses cluster at 2 g BID for prevention and 4 g/day for treatment cohorts.

Most randomized trials for prevention enrolled women at risk of GDM (e.g., prior GDM, family history, overweight/obesity, or PCOS) and started myo-inositol early (often at booking or 12–13 weeks). The modal regimen is 2,000 mg myo-inositol + ~200 µg folic acid, twice daily. Several trials and meta-analyses reported lower GDM incidence and improvements in OGTT glucose compared with placebo.

For treatment after a formal GDM diagnosis, evidence is smaller and includes prospective cohorts and pilot RCTs. A 2022 cohort of 330 women with GDM used 4,000 mg/day myo-inositol from diagnosis to delivery and reported lower fasting and post-dinner glucose, lower insulin requirements, and less neonatal hypoglycemia versus controls.

Evidence caveats. A 2023 Cochrane review concluded not enough evidence to support routine myo-inositol to prevent GDM, calling for larger, well-designed RCTs. Separately, a 2022 meta-analysis on prevention was retracted in 2023 and should not be used for decision-making. Treat all dosage claims online without citations as marketing, not guidance.

Visual summary

Typical study dosages and timing

Key points

• Prevention: 4 g/day total, split 2 g morning + 2 g evening, often with folic acid.
• Treatment: 4 g/day adjunct to diet, monitoring, and insulin as needed.

Prevention dosing used in trials

• Dose: 2 g myo-inositol twice daily (total 4 g/day).
• Co-nutrient: Folic acid ~200 µg twice daily in several Italian trials.
• Start: First antenatal visit or 12–13 weeks.
• Population: Prior GDM, family history of type 2 diabetes, overweight/obesity, or PCOS.
• Evidence signal: Lower GDM incidence and improved OGTT glucose in pooled RCTs, but heterogeneity and risk of bias remain.

First-trimester initiation aligns with a 2023 review suggesting 2–4 g/day from week 12–13 for prevention in high-risk pregnancies, though this is not a guideline.

Treatment dosing after GDM diagnosis

• Dose: 4 g/day myo-inositol adjunct to standard GDM care.
• Start: At diagnosis, continued to delivery.
• Reported effects: Lower fasting and post-prandial glucose, reduced insulin dose, lower neonatal hypoglycemia vs controls.

Evidence here is observational or small trials; use only with clinician oversight. PCOS supplements

Combinations and isomers

• Some studies tested D-chiro-inositol (DCI) 500 mg BID or MYO+DCI. Prevention benefits consistently appear with MYO 2 g BID, while low-dose MYO+DCI combinations can be ineffective. Data in pregnancy are limited; MYO remains the primary isomer studied.

Who might be considered in trials and what outcomes were tracked

Key points

• Trials often enrolled high-risk women.
• Outcomes included GDM incidence, OGTT values, insulin need, preeclampsia, preterm birth, and neonatal hypoglycemia.

Risk profiles studied. Enrollment frequently required one or more of: prior GDM, first-degree family history of type 2 diabetes, overweight/obesity, or PCOS.

Maternal outcomes. Several syntheses report reduced GDM incidence and lower fasting/1-h/2-h OGTT glucose with myo-inositol; some also suggest reduced insulin need and fewer hypertensive disorders. Certainty ranges from low to moderate and varies by analysis.

Neonatal outcomes. Signals include lower preterm birth and less neonatal hypoglycemia in some datasets, but not all analyses agree. The Cochrane review judged the evidence insufficient for a firm prevention recommendation.

If you need broader context on risks and targets, see our gestational diabetes guide.

Safety, quality, and clinician discussion points

Key points

• Trials report good short-term tolerability at 2–4 g/day in pregnancy.
• Guidelines have not endorsed routine myo-inositol for GDM prevention.

Across pregnancy RCTs and cohorts, myo-inositol at 2–4 g/day was generally well tolerated, with few adverse effects reported. However, supplements are not regulated like drugs, product quality varies, and long-term pregnancy safety data are limited.

Professional bodies have not issued strong recommendations to use myo-inositol to prevent GDM. The 2023 Cochrane review concluded current evidence is insufficient for routine prevention. If considered, it should be adjunctive to diet, activity, glucose monitoring, and pharmacotherapy when indicated.

A 2022 prevention meta-analysis that favored myo-inositol was retracted in 2023; disregard its dosage claims.

If you and your clinician decide to try it, consider split dosing and document glucose logs.
Optional: myo-inositol 2 g sachets — use only if approved by your clinician.