You're not imagining it. If you have PMOS (PCOS) and you're pregnant, or trying to be, chances are nobody sat you down and explained what insulin does to your body at this stage. You were probably told to 'watch your diet' and handed an appointment for a glucose test.

We also owe you a correction. An earlier version of this article said myo-inositol supplements can significantly lower the risk of gestational diabetes in pregnant women with PMOS (PCOS). The evidence has moved on, and the best trial so far says otherwise. A 2025 randomised trial of 464 pregnant women with PMOS (PCOS) found no difference in complications between myo-inositol and placebo [1]. We sell supplements that contain myo-inositol, so we'd rather tell you this plainly than let an old claim stand.

PCOS has been renamed PMOS (polyendocrine metabolic ovarian syndrome), and the NHS now uses the new name, so we use both here while the change beds in [2].

Here's what this guide covers: why PMOS (PCOS) raises the odds of some pregnancy complications, what the myo-inositol research shows, what UK and international guidelines say, how glucose testing works, and what the NHS advises you to take. Your diagnosis is a starting point, not a verdict, and none of this replaces your midwife or obstetric team.

In this guide:

• Why does PMOS (PCOS) raise the risk of pregnancy complications?
• What is myo-inositol, and why did it get attention?
• Does myo-inositol prevent complications in PMOS pregnancies?
• What about gestational diabetes in other pregnancies?
• What do the guidelines say about inositol?
• Is myo-inositol safe in pregnancy?
• How is glucose tested in pregnancy with PMOS (PCOS)?
• What helps with blood sugar in pregnancy?
• Which supplements does the NHS advise?
• Frequently asked questions

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Why Does PMOS (PCOS) Raise the Risk of Pregnancy Complications?

Start with insulin. Insulin resistance means your cells respond less well to insulin, so your pancreas makes more. In PMOS (PCOS), surrogate markers suggest it affects about 44% to 70% of women, and by the gold-standard clamp method it appears in about 75% of lean women and 95% of overweight women [3, 4]. Pregnancy adds its own insulin resistance, which is normal and helps send glucose to your baby. Stack the two together and glucose control can tip.

What does that look like in the numbers? A meta-analysis of 63 studies found women with PMOS (PCOS) had higher odds of gestational diabetes (OR 2.89), gestational hypertension (2.58), pre-eclampsia (1.87), miscarriage (1.59) and caesarean birth (1.39). Where studies matched women by BMI, the odds stayed raised for gestational diabetes (2.85), gestational hypertension (2.42), miscarriage (3.92) and caesarean (1.55), so weight isn't the whole story. The pre-eclampsia result in matched studies was borderline [5].

A larger 2024 meta-analysis of 104 studies and 106,690 pregnancies reached the same direction on miscarriage, gestational diabetes, hypertension, pre-eclampsia and caesarean, including in age- and BMI-matched analyses. The miscarriage odds ratio was 1.49 [6]. A US cohort of 14,882 deliveries with PMOS (PCOS) found adjusted odds of 2.19 for gestational diabetes, 1.47 for gestational hypertension and 1.29 for pre-eclampsia [7].

For context, about one in eight pregnancies in England was affected by gestational diabetes in 2022, up from about 8% in 2018 [8]. The draft NICE guideline lists higher risks of gestational diabetes, hypertension, pre-eclampsia, miscarriage, preterm delivery and low birth weight in PMOS (PCOS), and advises monitoring for them [9].

None of this is a prediction for you. Most pregnancies with PMOS (PCOS) go well. It's a reason to tell your midwife about your diagnosis early and ask about testing.

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What Is Myo-Inositol, and Why Did It Get So Much Attention?

Myo-inositol is a compound your body makes and that is also found in some foods. Inside cells it takes part in the signalling that follows insulin binding. That's the biology behind the idea that extra myo-inositol might improve insulin sensitivity.

The interest in PMOS (PCOS) began with a 1999 trial of a related molecule, D-chiro-inositol. In 44 obese women with PMOS (PCOS), 1,200 mg a day for six to eight weeks led to ovulation in 19 of 22 women against 6 of 22 on placebo, with lower free testosterone and triglycerides [10]. That's a different molecule, a short trial and a small sample, and it wasn't in pregnancy.

You'll also see the claim that women with PMOS (PCOS) have lower circulating myo-inositol. The evidence for that is weak. One study of 23 women with PMOS (PCOS) and 26 controls found that urinary clearance of D-chiro-inositol was about six times higher, but myo-inositol clearance did not differ [11]. So the 'low myo-inositol' story isn't established.

Since then, many small trials have looked at myo-inositol in PMOS (PCOS). A 2024 meta-analysis of 30 trials with 2,230 participants concluded that the evidence was limited and inconclusive: some metabolic measures may improve, but most of the evidence was of low or the lowest certainty [12].

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Does Myo-Inositol Prevent Complications in Pregnancies With PMOS (PCOS)?

This is the question the old article claimed to answer, and the 2025 MYPP trial is the direct test. It was a double-blind, placebo-controlled trial at 13 Dutch hospitals. Women with PMOS (PCOS) joined at 8 to 16 weeks and took either 2 g of myo-inositol with 0.2 mg folic acid, or folic acid alone, twice a day until delivery. That's 4 g of myo-inositol a day, double what most supplements contain [1].

The main result was a risk ratio of 0.93 (95% confidence interval 0.68 to 1.28, P = 0.67), which means no clear difference. Gestational diabetes, pre-eclampsia, preterm birth and HbA1c didn't differ significantly either. The only statistically significant difference was fewer planned caesareans, which the authors thought could be chance because overall caesarean rates were the same [1].

The trial had limits. Fewer women had the main outcome than the researchers expected, only about 39% of the myo-inositol group took at least 80% of their doses, and baseline hyperandrogenism was higher in the myo-inositol group. The authors still judged that a clinically relevant benefit was unlikely to have been missed. Their conclusion: myo-inositol should not be recommended as dietary advice for pregnant women with PMOS (PCOS) [1].

It's one trial, and science will keep moving. But it's the largest and best-designed trial in this exact group, so it carries a lot of weight.

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What About Myo-Inositol and Gestational Diabetes in Other Pregnancies?

The older claims came from trials in other groups of pregnant women, not from PMOS (PCOS). A 2023 Cochrane review pooled 7 trials with 1,319 women, mostly from Italy. Gestational diabetes was lower with myo-inositol (risk ratio 0.53, 95% CI 0.31 to 0.90 in 6 trials), as were hypertensive disorders and preterm birth. But the authors rated the certainty of evidence as low or lower and concluded there is not enough evidence that myo-inositol prevents gestational diabetes [13].

The review also found results that cut the other way, such as a higher (but statistically uncertain) rate of neonatal hypoglycaemia (RR 3.07, 95% CI 0.90 to 10.52) and of large-for-gestational-age babies (RR 1.40, 0.65 to 3.02) [13]. Those are wide intervals from small studies, so they aren't proof of harm, but they aren't reassurance either.

Individual trials disagree. An open-label Italian trial of 220 women with a parent who had type 2 diabetes found gestational diabetes in 6% on myo-inositol against 15.3% on folic acid alone [14]. A later trial of 240 women with a family history of diabetes found 23% against 18% with no benefit, using a combined inositol product [15]. A 2019 meta-analysis of 5 trials found a pooled odds ratio of 0.49 with a confidence interval (0.24 to 1.03) that included no effect [16].

So the honest summary is mixed, small and low certainty in general pregnancy, and negative in the one large trial in PMOS (PCOS).

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What Do UK and International Guidelines Say About Inositol?

• The 2023 international guideline says inositol, alone or with other therapies, should be considered experimental in PMOS (PCOS) [17].
• The draft NICE guideline (consultation closed 11 August 2026, final version expected December 2026) advises that there is uncertainty about the clinical benefit of inositol for metabolic health problems, and that inositol is not effective for fertility problems. Its pregnancy section mentions metformin but makes no recommendation for inositol [9].
• The 2024 meta-analysis behind the guideline update called the evidence limited and inconclusive [12].

What about metformin? The draft NICE guideline says to consider it in pregnancy for people with extra risk factors, mainly to reduce preterm delivery and limit weight gain, and to explain that it hasn't been shown to prevent gestational diabetes [9]. The PregMet2 trial agrees: gestational diabetes was 25% on metformin against 24% on placebo, and the lower rate of late miscarriage or preterm birth (5% against 10%) wasn't statistically significant [18].

There's also no authorised UK health claim for inositol, so you'll never see a compliant claim that it supports blood sugar or pregnancy.

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Is Myo-Inositol Safe in Pregnancy?

In the Cochrane review, five trials measured adverse effects and reported none attributed to myo-inositol, and two didn't report them [13]. In the MYPP trial, any potential adverse effect occurred in 6.9% of women on myo-inositol and 9.1% on placebo, and nausea was the most common difference (3.2% against 5.9%) [1].

That's reassuring, but it isn't a safety statement. I couldn't find any NHS, MHRA or EFSA statement on inositol in pregnancy. The NHS advice that applies to everything is to check with your midwife, doctor or pharmacist before taking any supplement or herbal product in pregnancy, because not all 'natural' products are safe [19].

So don't start or stop anything on the strength of this article. If you're already taking a myo-inositol supplement, tell your midwife or obstetric team, and decide together. The trial authors' conclusion is that it shouldn't be recommended to prevent complications, but that doesn't mean you need to panic if you've been taking it.

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How Is Glucose Tested in Pregnancy With PMOS (PCOS)?

The 2023 guideline says a 75 g oral glucose tolerance test (OGTT) should be considered in all women with PMOS (PCOS) who don't already have diabetes when planning pregnancy or seeking fertility treatment. If it wasn't done before conception, it could be offered at the first prenatal visit, and all women with PMOS (PCOS) should be offered it at 24 to 28 weeks [17].

In the UK, NICE's diabetes in pregnancy guideline lists risk factors for testing as BMI over 30, a previous baby of 4.5 kg or more, previous gestational diabetes, a first-degree relative with diabetes, and a family origin with a high prevalence of diabetes. PMOS (PCOS) isn't on that list, so ask your midwife directly whether you can be tested, and whether earlier is appropriate [20].

An earlier version of this article told you to ask for fasting insulin and HOMA-IR. We've removed that. The 2023 guideline says clinically available insulin assays are of limited relevance and shouldn't be used in routine care, and the draft NICE guideline offers HbA1c or fasting glucose plus a lipid profile instead [17, 9]. Glucose testing is the route that changes care.

If you get a result you don't understand, ask what the thresholds are. NICE's gestational diabetes thresholds are a fasting glucose of 5.6 mmol/L or above, or a two-hour value of 7.8 mmol/L or above [20].

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What Helps With Blood Sugar in Pregnancy With PMOS (PCOS)?

NICE's nutrition in pregnancy guidance says you don't need a special diet or to 'eat for two', that you can continue or gradually increase physical activity and limit long periods of sitting, and that intentional weight loss isn't recommended during pregnancy [21].

Will diet and exercise stop gestational diabetes? A Cochrane review of 11 trials and 3,744 women found no significant reduction (RR 0.92, 95% CI 0.68 to 1.23) [22]. That doesn't mean healthy habits are pointless. They support your wellbeing, energy and recovery, but they aren't a guarantee, and a diagnosis isn't a failure on your part.

If you're told you have gestational diabetes, your team will usually advise glucose monitoring, and medicines such as metformin or insulin if needed. Ask for a dietitian referral, because food advice in pregnancy needs to be tailored. For wider background, see our guide to PMOS (PCOS) and diabetes.

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Which Supplements Does the NHS Advise in Pregnancy?

These are the NHS basics [23]:

• Folic acid: 400 micrograms a day from before conception until 12 weeks. A 5 mg dose is prescribed for some people, including those with a neural tube defect history or diabetes. The old BMI cut-off for 5 mg has been dropped.
• Vitamin D: 10 micrograms a day from early October to late March, and all year for some groups. Don't exceed 100 micrograms a day.
• Vitamin A: don't take cod liver oil or supplements containing vitamin A (retinol).
• Anything else: check with your midwife, doctor or pharmacist first [19].

Read this first. Pregnancy is a food supplement. It isn't a treatment for PMOS (PCOS) or gestational diabetes, and it doesn't replace your midwife's advice or a prescribed 5 mg folic acid dose. It contains myo-inositol, which the evidence above doesn't show prevents pregnancy complications, so don't choose it for that reason. Check the label against the NHS advice on folic acid and vitamin A, and show it to your midwife, doctor or pharmacist before you start.

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Frequently Asked Questions

Can myo-inositol prevent gestational diabetes in PMOS (PCOS)?

The best trial in pregnant women with PMOS (PCOS), 464 women, found no difference in gestational diabetes (17.0% against 15.8%) or other complications. A Cochrane review of other pregnancies rated the evidence as low certainty or lower [1, 13].

Is myo-inositol safe during pregnancy?

Trials reported no adverse effects attributed to it, but the evidence is small and low quality, and I couldn't find an NHS or MHRA safety statement. Check with your midwife or doctor before taking it [13, 19].

Should I stop taking myo-inositol if I'm pregnant?

That's a decision to make with your midwife or obstetric team. The trial authors say it shouldn't be recommended as dietary advice in pregnancy with PMOS (PCOS), and the draft NICE guideline makes no recommendation for it in pregnancy [1, 9].

When should I be tested for gestational diabetes with PMOS (PCOS)?

The 2023 guideline recommends offering a 75 g glucose tolerance test at 24 to 28 weeks, and earlier if not done before conception. PMOS (PCOS) isn't a NICE risk factor, so ask your midwife about earlier testing [17, 20].

Does PMOS (PCOS) increase pregnancy risks?

Yes, on average. Meta-analyses show higher odds of miscarriage, gestational diabetes, hypertension, pre-eclampsia and caesarean birth, even in BMI-matched studies, though most pregnancies go well [5, 6].

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The Bottom Line

PMOS (PCOS) raises the odds of some pregnancy complications, and that's worth taking seriously. But the best trial in this exact group found that myo-inositol doesn't reduce them, the Cochrane evidence in other pregnancies is low certainty, and the draft NICE guideline says its benefit is uncertain. What does matter: telling your midwife about your diagnosis, getting a glucose test, taking folic acid and vitamin D as the NHS advises, and getting your questions answered.

Your body is trying to tell you something, and what it needs is a team that listens. Hormonal literacy isn't complicated, it's just rarely taught. It's not a magic fix, and we'd rather tell you that than sell you one.

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Related Reading

• PMOS (PCOS) and Diabetes: What Your Risk Looks Like
• PMOS (PCOS) and Insulin Resistance: Understanding the Link
• The Role of Myo-Inositol in Fertility Treatments: What the Research Actually Shows
• The Best Supplements for PCOS: What the Research Actually Says
• How to Improve Fertility With PMOS (PCOS): 6 Habits
• Blood Sugar Balance: An Underrated Tool for Women's Hormone Health

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This article is for educational purposes only and does not constitute medical advice. Guidance details are accurate to the sources cited at the time of writing and may change when NICE publishes its final PMOS guideline. MyOva products are food supplements, not medicines, and are not intended to diagnose, treat, cure or prevent any disease. Food supplements should not replace a varied diet. If you are pregnant or planning a pregnancy, speak to your midwife, GP or obstetric team before taking any supplement.

References

1. 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. 2025;334(13):1151-1159. doi:10.1001/jama.2025.13668
2. NHS. Polyendocrine metabolic ovarian syndrome (PMOS), formerly polycystic ovary syndrome (PCOS). Last reviewed 30 June 2026. https://www.nhs.uk/conditions/polyendocrine-metabolic-ovarian-syndrome-pmos/
3. Diamanti-Kandarakis E, Dunaif A. Insulin resistance and the polycystic ovary syndrome revisited: an update on mechanisms and implications. Endocr Rev. 2012;33(6):981-1030. doi:10.1210/er.2011-1034
4. Stepto NK, Cassar S, Joham AE, et al. Hum Reprod. 2013;28(3):777-784. doi:10.1093/humrep/des463 (hyperinsulinaemic-euglycaemic clamp study; title not confirmed here)
5. Bahri Khomami M, Joham AE, Boyle JA, et al. Increased maternal pregnancy complications in polycystic ovary syndrome appear to be independent of obesity: a systematic review, meta-analysis, and meta-regression. Obes Rev. 2019;20(5):659-674. doi:10.1111/obr.12829
6. Bahri Khomami M, et al. Pregnancy complications in polycystic ovary syndrome: meta-analysis. Nat Commun. 2024;15:5591. doi:10.1038/s41467-024-49749-1 (title and full author list not confirmed here)
7. Mills G, Badeghiesh A, Suarthana E, Baghlaf H, Dahan MH. US cohort study of pregnancy outcomes in polycystic ovary syndrome. Hum Reprod. 2020;35(7):1666-1674. doi:10.1093/humrep/deaa099 (title not confirmed here)
8. King's College London. One in eight mothers diagnosed with gestational diabetes (news release on a study in BMJ Medicine 2026;5(1):e002412). https://www.kcl.ac.uk/news/one-in-eight-mothers-diagnosed-with-gestational-diabetes
9. National Institute for Health and Care Excellence. Polycystic ovary syndrome (PMOS): draft guideline for consultation (GID-NG10436), July 2026. Final publication expected December 2026. https://www.nice.org.uk/guidance/indevelopment/gid-ng10436
10. Nestler JE, Jakubowicz DJ, Reamer P, Gunn RD, Allan G. Ovulatory and metabolic effects of D-chiro-inositol in the polycystic ovary syndrome. N Engl J Med. 1999;340(17):1314-1320. doi:10.1056/NEJM199904293401703
11. Baillargeon JP, et al. Altered D-chiro-inositol urinary clearance in women with polycystic ovary syndrome. Diabetes Care. 2006;29(2):300-305
12. Fitz V, Graca S, Mahalingaiah S, et al. Inositol for polycystic ovary syndrome: a systematic review and meta-analysis to inform the 2023 update of the international evidence-based PCOS guidelines. J Clin Endocrinol Metab. 2024;109(6):1630-1655. doi:10.1210/clinem/dgad762
13. Motuhifonua SK, Lin L, Alsweiler J, Crawford TJ, Crowther CA. Antenatal dietary supplementation with myo-inositol for preventing gestational diabetes. Cochrane Database Syst Rev. 2023;(2):CD011507. doi:10.1002/14651858.CD011507.pub3
14. D'Anna R, Scilipoti A, Caruso C, et al. Myo-inositol supplementation and onset of gestational diabetes mellitus in pregnant women with a family history of type 2 diabetes. Diabetes Care. 2013;36(4):854-857. doi:10.2337/dc12-1371
15. Farren M, et al. Diabetes Care. 2017;40(6):759-763 (randomised trial of myo-inositol in women at risk of gestational diabetes; volume and pages not confirmed here)
16. Vitagliano A, Saccone G, Cosmi E, et al. Inositol for the prevention of gestational diabetes: a systematic review and meta-analysis of randomized controlled trials. Arch Gynecol Obstet. 2019;299(1):55-68. doi:10.1007/s00404-018-5005-0
17. Teede HJ, Tay CT, Laven JJE, et al. Recommendations from the 2023 international evidence-based guideline for the assessment and management of polycystic ovary syndrome. Hum Reprod. 2023;38(9):1655-1679. doi:10.1093/humrep/dead156
18. Løvvik TS, et al. PregMet2 trial of metformin in pregnancy in polycystic ovary syndrome. Lancet Diabetes Endocrinol. 2019 (volume and pages not confirmed here)
19. NHS. Medicines in pregnancy. Last reviewed 5 September 2022. https://www.nhs.uk/pregnancy/keeping-well/medicines/
20. National Institute for Health and Care Excellence. Diabetes in pregnancy: management from preconception to the postnatal period (NG3). https://www.nice.org.uk/guidance/ng3
21. National Institute for Health and Care Excellence. Maternal and child nutrition (NG247), recommendations 1.1.5 and 1.1.6. https://www.nice.org.uk/guidance/ng247
22. Bain E, Crane M, Tieu J, Han S, Crowther CA, Middleton P. Diet and exercise interventions for preventing gestational diabetes mellitus. Cochrane Database Syst Rev. 2015;(4):CD010443
23. NHS. Pregnancy vitamins and supplements. https://www.nhs.uk/pregnancy/keeping-well/pregnancy-vitamins-and-supplements/

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References