Myo-inositol in pregnancy and gestational diabetes - what Cochrane says
Myo-inositol in pregnancy and gestational diabetes: a reliable answer based on research. u Bucha.
Gestational diabetes (GDM) affects 7 to 14% of pregnant women in Europe and is associated with an increased risk of fetal macrosomia, cesarean section, and later type 2 diabetes in both mother and child. Myo-inositol - a natural metabolite involved in insulin signaling - has been studied for a decade as a supplement to reduce the risk of GDM. The Cochrane review by Crawford et al. including randomized clinical trials showed a reduction in the risk of gestational diabetes with myo-inositol supplementation (RR about 0.43-0.57) - with moderate certainty of evidence (Crawford et al., Cochrane, 2015). This article explains what this means for pregnant women and when supplementation may make sense.
KEY INFORMATION
• The Cochrane review showed a reduction in the risk of GDM with myo-inositol - RR about 0.43-0.57 - with moderate certainty of evidence (Crawford et al., Cochrane, 2015).
• The dose used in studies: 4 g daily (2 × 2 g) from the first trimester throughout the pregnancy.
• Myo-inositol works by improving insulin sensitivity, not by lowering glucose like medications.
• Safety has been confirmed in studies up to 40 weeks of pregnancy - but supplementation should always be discussed with the attending physician.
What is myo-inositol and how does it work in pregnancy?
Inositol is a molecule structurally similar to glucose, naturally present in the body and in many food products - fruits, legumes, nuts. There are several isomers of inositol, of which myo-inositol is the most biologically active and best studied. In cells, it functions as a second messenger in insulin signaling - when insulin binds to the receptor, myo-inositol participates in transmitting the signal inside the cell, facilitating glucose transport (Croze and Meste, Biochimie, 2013).
In pregnancy, insulin resistance physiologically increases - especially in the second and third trimesters - which is a normal adaptation facilitating glucose delivery to the fetus. In women predisposed to metabolic disorders, this insulin resistance may exceed the threshold and progress to gestational diabetes. Myo-inositol, by improving cell sensitivity to insulin, may limit this excessive increase in insulin resistance and reduce the risk of GDM.
The diet provides an average of 1-2 g of inositol daily. Therapeutic doses used in pregnancy studies are 4 g daily - two to four times more than from diet. Hence the need for supplementation to achieve a preventive effect.
What exactly did the Cochrane review show?
Crawford et al. conducted a systematic Cochrane review of randomized studies evaluating inositol in pregnant women or women planning pregnancy (Cochrane Database, 2015). The review included several RCTs with over 500 participants in total. Key findings regarding GDM: the risk of gestational diabetes was significantly lower in groups supplementing with myo-inositol.
| Outcome | Direction of effect | Certainty of evidence |
|---|---|---|
| Risk of gestational diabetes (GDM) | Reduction RR about 0.43-0.57 | Moderate |
| Fasting glucose | Lower in the inositol group | Low-moderate |
| Fetal macrosomia | Trend towards reduction (inconsistent) | Niska |
| Adverse effects for the mother | No significant differences vs placebo | Moderate |
| Adverse effects for the child | No significant differences vs placebo | Moderate |
Cochrane authors' assessment: the results are promising, but the evidence base is still insufficient for population recommendations. The studies were relatively small (50-300 participants) and conducted mainly in Italy. Large multicenter RCTs from various populations are needed before mio-inositol can be included in standard prenatal guidelines.
We noted while analyzing original Italian studies (Matarrelli et al., D’Anna et al.) that the effects were particularly pronounced in women with elevated BMI and those with a previous history of GDM. This suggests that myo-inositol may work best in women with existing insulin resistance - rather than as a supplement "for everyone". Target group selection is important for assessing effectiveness.
Mio-inozytol a PCOS - dodatkowy kontekst
Women with polycystic ovary syndrome (PCOS) have an increased risk of both infertility and gestational diabetes. Myo-inositol is one of the better-studied supplements in women with PCOS - meta-analyses confirm improvements in ovulation, reductions in androgens, and improvements in insulin sensitivity (Unfer et al., Gynecol Endocrinol, 2016). In the context of pregnancy in women with PCOS, myo-inositol may act in two ways - supporting both the course of pregnancy and reducing the risk of GDM resulting from existing insulin resistance.
How to differentiate mio-inositol from D-chiro-inositol? These are two different isomers sometimes sold interchangeably. Mio-inositol is the physiologically dominant form and better studied in pregnancy. D-chiro-inositol is more effective for PCOS, but in too high doses, it can paradoxically reduce egg quality. Combined supplements (mio-inositol:D-chiro ratio = 40:1, mimicking the physiological proportion) are used in PCOS protocols, but for the prevention of GDM alone, mio-inositol is sufficient.
Practical tips for pregnant women considering mio-inositol
If you are in the high-risk group for GDM - with obesity, PCOS, a history of gestational diabetes, or a family history of diabetes - myo-inositol is a supplement worth discussing with your gynecologist or midwife at one of your first prenatal visits. The evidence is promising, though not sufficient for population-wide recommendations for all pregnant women.
Standard questions to ask your doctor before starting: is your risk of GDM elevated? Is myo-inositol appropriate alongside other prenatal supplements you are taking? When is the best time to start - the first trimester provides the largest preventive window, as GDM is usually diagnosed between 24 and 28 weeks of pregnancy. Starting earlier allows more time for the metabolic effect.
Frequently Asked Questions
What is mio-inositol and why is it used in pregnancy?
Myo-inositol is a natural isomer of inositol, naturally present in many tissues and foods. During pregnancy, it is mainly supplemented due to its role in insulin signaling - it improves cell sensitivity to insulin, which may reduce the risk of gestational diabetes. It is also being studied as a supplement to folic acid in the prevention of neural tube defects (Croze and Meste, Biochimie, 2013).
What does the Cochrane review say about inositol in pregnancy?
A Cochrane review showed a reduction in the risk of gestational diabetes with myo-inositol supplementation - RR about 0.43-0.57 in high-quality studies. The authors assess the strength of evidence as moderate and recommend further large studies before introducing it into standard prenatal recommendations (Crawford et al., Cochrane, 2015).
What dose of mio-inositol is used in pregnancy studies?
Pregnancy studies most commonly used 4 g of mio-inositol daily, divided into two doses of 2 g (morning and evening), usually from the first trimester throughout the pregnancy. Some protocols combined 2 g of mio-inositol with 200 µg of folic acid (Crawford et al., Cochrane, 2015).
Is mio-inositol safe in pregnancy?
Clinical studies up to 40 weeks of pregnancy did not show adverse effects for the mother or child at a dose of 4 g daily. Mio-inositol is naturally present in the body. Nevertheless, due to the limited number of large safety studies, its use in pregnancy should be discussed with the attending gynecologist (Crawford et al., Cochrane, 2015).
Who can particularly benefit from mio-inositol in pregnancy?
Women at increased risk of GDM - with obesity (BMI over 30), gestational diabetes in a previous pregnancy, polycystic ovary syndrome, or a family history of diabetes. In women with PCOS, myo-inositol is particularly well-studied due to its association with insulin resistance (Unfer et al., Gynecol Endocrinol, 2016).
Does mio-inositol also prevent neural tube defects?
Preliminary data suggest that myo-inositol may complement the action of folic acid in cases of neural tube defects resistant to folates. The evidence is still insufficient for population recommendations, and myo-inositol should not be considered a substitute for folic acid (Croze and Meste, Biochimie, 2013).
Is dietary inositol sufficient during pregnancy?
The diet provides about 1-2 g of inositol daily from fruits, vegetables, legumes, and nuts. The doses used in pregnancy studies (4 g daily) are 2-4 times higher than typical dietary intake - hence the need for supplementation to achieve a preventive effect (Crawford et al., Cochrane, 2015).
How does myo-inositol affect blood sugar levels during pregnancy?
Myo-inositol acts as a second insulin messenger - it improves the cellular response to insulin without directly lowering glucose like medications. In studies, women supplementing with myo-inositol had lower fasting glucose levels and glucose tolerance test results (OGTT 75 g) compared to placebo. The effect is preventive, not therapeutic (Croze and Meste, Biochimie, 2013).
Should myo-inositol and folic acid be taken together?
Several Italian RCTs used a combined supplementation protocol: 2 g of myo-inositol with 200 µg of folic acid twice daily. Folic acid in pregnancy is recommended by all perinatal guidelines as a mandatory supplement to reduce the risk of neural tube defects. Myo-inositol does not replace folic acid - both supplements work through different mechanisms and can be taken together. The studies by D’Anna et al. used this combination and showed a reduction in the risk of GDM with good tolerance (D’Anna i in., Diabetes Care, 2013). Before starting any supplement during pregnancy, discuss the dosage with your gynecologist - to avoid duplicating ingredients with the prenatal preparation.
How does myo-inositol work in women with PCOS before pregnancy?
In women with PCOS planning pregnancy, myo-inositol has well-documented cycle-regulating and ovulation-improving effects. A meta-analysis by Unfer et al. (2016) covering 23 clinical studies showed that myo-inositol (2-4 g daily) improved hormonal parameters, lowered androgens, and supported menstrual regularity (Unfer et al., Gynecol Endocrinol, 2016). Women with PCOS who become pregnant have a higher risk of GDM - therefore, continuing myo-inositol after confirming pregnancy (after consulting with a doctor) may make sense both as a continuation of metabolic support and GDM prevention.
This article is for informational and educational purposes and does not replace consultation with a doctor. If you are pregnant, breastfeeding, taking medications, or have chronic conditions, consult the use of supplements or herbs with a specialist.
Author: Michał Waluk · Published: 2026-05-04 · Updated: 2026-05-04
