Gestational diabetes is high blood sugar first found in pregnancy, usually by a test at 24 to 28 weeks; 3% to 20% of pregnant women develop it. Here is exactly how it is diagnosed in Canada, the targets guidelines set, what treatment trials found and what lowers the risk of type 2 diabetes afterwards.
Gestational diabetes is diabetes first diagnosed in the second or third trimester of pregnancy that was not clearly present before the pregnancy 1. Between 3% and 20% of pregnant women develop it, depending on their risk factors, and Diabetes Canada advises screening everyone without known diabetes at 24 to 28 weeks 2. It usually causes no symptoms, so a blood test is how it is found 7.
Untreated, it leads to more problems for mother and baby, and treatment reduces them 2. It usually goes away after delivery 8 but leaves a much higher chance of type 2 diabetes 6. Glucose is given in mmol/L with mg/dL in brackets; see mmol/L and mg/dL to convert.
Gestational diabetes happens when pregnancy hormones make the body’s cells use insulin less well and the pancreas can’t make enough extra insulin to make up for it 7, 9.
The placenta, the organ that nourishes the baby, makes hormones including estrogen, cortisol and human placental lactogen. Johns Hopkins Medicine notes that these can block insulin’s effect, which usually begins about 20 to 24 weeks into pregnancy 9. The ADA’s 2026 Standards of Care describe early pregnancy as a time when insulin may work better, followed by progressive insulin resistance in the second and third trimesters 3.
Most pregnant women can make enough extra insulin to overcome this resistance; gestational diabetes develops when the body can’t 7. Because insulin sensitivity falls so much in pregnancy, Diabetes Canada notes that not every case can be prevented 2. Our article on insulin resistance explains the mechanism. Symptoms, if any, are usually mild, such as being thirstier than normal or urinating more often 7.
In plain terms: The placenta makes hormones that work against insulin, and the effect grows as pregnancy goes on. If your pancreas can’t make enough extra insulin to keep up, glucose rises. That is why gestational diabetes is usually found in the second half of pregnancy.
Any pregnant woman can develop gestational diabetes 9, but Diabetes Canada lists these factors as raising the risk 2:
These factors are common: Yale Medicine notes that about 90% of pregnant women have at least one risk factor for diabetes 8. Diabetes Canada supports universal screening, meaning a test for every pregnant woman without known diabetes 2. Rates depend on risk factors and on the test used 2. Johns Hopkins Medicine puts the US figure at about 3% to 8% of pregnant women 9, and the ADA reports a dramatic increase 3.
Diabetes Canada’s preferred approach has two steps: a 50 g glucose challenge test between 24 and 28 weeks, followed by a 75 g oral glucose tolerance test (OGTT) if the first result is abnormal 2. Its alternate approach goes straight to a 75 g OGTT with lower cut-offs 2.
For the challenge test, you drink a sweet glucose liquid and blood is drawn one hour later; you don’t need to fast 10. A result of 11.1 mmol/L (200 mg/dL) or higher counts as gestational diabetes with no second test; a lower but abnormal result leads to the OGTT 2. In the United States, 7.8 mmol/L (140 mg/dL) or more may mean returning for an OGTT 10.
For the OGTT, you fast for at least 8 hours 10. Glucose is measured fasting and one and two hours after the 75 g drink, and a single value at or above any cut-off confirms gestational diabetes 2.
| Test | Preferred two-step approach | Alternate one-step approach |
|---|---|---|
| 50 g challenge test, 1 hour | 11.1 mmol/L (200 mg/dL) or more is gestational diabetes; an abnormal lower result leads to the OGTT 2 | Not used 2 |
| 75 g OGTT, fasting | 5.3 mmol/L (95 mg/dL) or more 2 | 5.1 mmol/L (92 mg/dL) or more 2, 11 |
| 75 g OGTT, 1 hour | 10.6 mmol/L (191 mg/dL) or more 2 | 10.0 mmol/L (180 mg/dL) or more 2, 11 |
| 75 g OGTT, 2 hours | 9.0 mmol/L (162 mg/dL) or more 2 | 8.5 mmol/L (153 mg/dL) or more 2, 11 |
| Share of the HAPO study group meeting at least one OGTT cut-off | 8.8% 2 | 16.1% 2 |
Both sets come from the HAPO study, described below, which found that risk rose steadily with glucose 12. The one-step cut-offs, from the International Association of the Diabetes and Pregnancy Study Groups (IADPSG), are the values linked to 1.75 times the odds of a large baby, high newborn body fat or a high cord-blood C-peptide, a marker of the baby’s own insulin 2. The Endocrine Society’s 2013 guideline recommends them 11. Diabetes Canada’s preferred cut-offs match twice the odds, so fewer women meet them 2. Diabetes Canada notes that a 2013 US National Institutes of Health panel found not enough evidence to adopt the one-step approach, and that national guidelines still differ 2.
If you are at high risk of undiagnosed type 2 diabetes, Diabetes Canada advises an A1c test before 20 weeks 2. It notes that a first-trimester A1c of 5.9% or higher appears to carry a risk of problems in pregnancy, later gestational diabetes and diabetes after birth 2.
The usual targets are below 5.3 mmol/L (95 mg/dL) fasting, and below 7.8 mmol/L (140 mg/dL) one hour or below 6.7 mmol/L (120 mg/dL) two hours after a meal 2, 3.
Diabetes Canada notes that good outcomes have been reported with these targets 2, and the ADA’s 2026 goals match: fasting below 5.3 mmol/L, plus either the one-hour or the two-hour goal 3. For people treated with insulin, the ADA adds lower limits of 3.9 mmol/L (70 mg/dL) fasting, 6.1 mmol/L (110 mg/dL) at one hour and 5.6 mmol/L (100 mg/dL) at two hours 3. Diabetes Canada says glucose can normally fall below 4.0 mmol/L (72 mg/dL) in pregnancy, but that women taking insulin should stay above 3.7 mmol/L (67 mg/dL) to avoid repeated lows 2. See low blood sugar for signs and treatment.
Diabetes Canada calls frequent self-monitoring essential and recommends checking both fasting and after meals 2; Mayo Clinic notes that your team may ask for four or more checks a day 13.
A continuous glucose monitor (CGM) is a sensor worn on the skin that measures glucose every few minutes. The ADA recommends CGM in pregnancy with type 1 diabetes, aiming for more than 70% of readings between 3.5 and 7.8 mmol/L (63 and 140 mg/dL) 3. For gestational diabetes, it says there are insufficient data to support CGM for everyone, and that one randomized trial comparing CGM with finger-stick checks found no significant difference in a combined measure of problems for mother and baby 3. Diabetes Canada’s 2018 guideline describes a trial of 340 women in which periodic CGM, compared with finger-stick checks alone, went with less preeclampsia, fewer first caesarean births and lower birth weights 2. Our comparison of CGMs and meters explains the trade-offs.
Treatment starts with changes to eating and physical activity, and medicine, such as insulin, is added if glucose stays above target 2, 3. The ADA says lifestyle change may suffice for many people: studies suggest 70% to 85% of those diagnosed under one widely used set of criteria (Carpenter-Coustan) manage with lifestyle alone, and the share may be higher with the lower IADPSG cut-offs 3.
The Endocrine Society recommends medical nutrition therapy, a personalized eating plan, for everyone with gestational diabetes 11. Carbohydrate is limited, not removed: Diabetes Canada advises at least 175 g a day, spread over meals and snacks 2, the same minimum the ADA gives for all pregnant people, along with at least 71 g of protein and 28 g of fibre 3. See how to count carbs.
The ADA says generally healthy people should do at least 150 minutes of moderate-intensity aerobic activity a week during pregnancy and after birth 3. Diabetes Canada encourages physical activity in gestational diabetes unless there is an obstetric reason not to 2.
Guidelines differ on the choice. Diabetes Canada lists insulin or metformin if targets aren’t met 2. The ADA calls insulin the first-line medicine in the United States and doesn’t recommend metformin or glyburide first, because both cross the placenta and data on long-term safety for children are of some concern 3. In one follow-up study, nine-year-olds exposed to metformin were heavier than those exposed to insulin in one of its two groups 3. Which medicine and dose is a decision for your prescriber.
Women with gestational diabetes have a higher risk of preeclampsia, a serious blood pressure problem of pregnancy 8. The Centers for Disease Control and Prevention (CDC) lists urgent warning signs for pregnancy and the year after delivery and says to “seek medical care immediately” for any of them 14. They include a headache that won’t go away or gets worse, dizziness or fainting, changes in vision, a fever of 38°C (100.4°F) or higher, extreme swelling of the hands or face, trouble breathing, chest pain or a fast-beating heart, severe belly pain that doesn’t go away, the baby’s movements stopping or slowing, and vaginal bleeding or fluid leaking during pregnancy 14. Cleveland Clinic advises contacting your provider if glucose is high several readings in a row or consistently low, or if illness stops you from following your plan 15.
Yes: two large randomized trials found that treating gestational diabetes lowered the risk of serious birth complications, very large babies and shoulder dystocia, where a baby’s shoulder gets stuck during delivery 4, 5.
The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study gave a 75 g OGTT at 24 to 32 weeks to 25,505 pregnant women at 15 centres in nine countries 12. Each rise of about 0.4 mmol/L (6.9 mg/dL) in fasting glucose, one standard deviation, went with 1.38 times the odds of a birth weight above the 90th percentile and 1.55 times the odds of a high cord-blood C-peptide 12. The links were continuous, even below levels diagnostic of diabetes, with no clear point where risk jumped 12.
The ACHOIS trial randomly assigned 1,000 women with gestational diabetes at 24 to 34 weeks to treatment (dietary advice, blood glucose monitoring and insulin as needed) or routine care 4. Serious perinatal complications, defined as death, shoulder dystocia, bone fracture or nerve palsy, fell from 4% to 1% (adjusted relative risk 0.33) 4. Treatment brought more labour inductions (39% versus 29%) and more admissions to the neonatal nursery (71% versus 61%), but no difference in caesarean births 4.
A 2009 trial randomly assigned 958 women with mild gestational diabetes, meaning an abnormal OGTT but fasting glucose below 5.3 mmol/L (95 mg/dL), to treatment or a control group 5. Its main combined outcome, which included stillbirth and newborn complications such as low blood sugar, did not differ significantly (32.4% versus 37.0%) 5. But treatment reduced birth weights above 4,000 g (5.9% versus 14.3%), shoulder dystocia (1.5% versus 4.0%), caesarean delivery (26.9% versus 33.8%) and preeclampsia or high blood pressure of pregnancy (8.6% versus 13.6%) 5.
Gestational diabetes usually goes away after delivery 8, but guidelines advise a 75 g OGTT within months and regular diabetes testing for life 2, 3. Diabetes Canada advises the OGTT between 6 weeks and 6 months after birth, then testing before any future pregnancy and every 3 years, or more often depending on risk 2. The ADA recommends it at 4 to 12 weeks after birth and lifelong screening for type 2 diabetes or prediabetes every 1 to 3 years 3.
A 2020 BMJ meta-analysis of 20 studies, covering 67,956 women with gestational diabetes and 1,264,417 without, found a relative risk of type 2 diabetes of 9.51, almost 10 times higher 6. Among women who had gestational diabetes, 9.22% developed type 2 diabetes in studies lasting one to five years and 16.15% in studies lasting more than 10 years, against 1.90% of controls in the longest studies 6. An earlier 2009 Lancet meta-analysis found a sevenfold higher risk (relative risk 7.43) 6. In the HAPO follow-up, 10 to 14 years after pregnancy, 52.2% of mothers who met the one-step criteria had type 2 diabetes or prediabetes, against 20.1% of those who did not 16.
Diabetes Canada encourages breastfeeding right after birth and for at least 4 months 2, and the ADA says breastfeeding reduces the risk of type 2 diabetes after gestational diabetes 3. In a cohort of 1,035 women with recent gestational diabetes, 113 (11.8%) developed diabetes within two years 17. Exclusive breastfeeding at six to nine weeks went with roughly half the risk of exclusive formula feeding (adjusted hazard ratio 0.46), and breastfeeding for more than 10 months with a hazard ratio of 0.43 against 0 to 2 months 17. As an observational study, it shows a link, not proof of cause.
In the Diabetes Prevention Program, 350 women with past gestational diabetes and a raised BMI, raised fasting glucose and impaired glucose tolerance were randomly assigned to an intensive lifestyle program, metformin or placebo 18. Over 10 years, lifestyle reduced progression to diabetes by 35% and metformin by 40%, compared with placebo 18. The ADA recommends intensive lifestyle programs and/or metformin for people with overweight or obesity and prediabetes after gestational diabetes 3.
In Canada’s preferred approach, one 75 g OGTT value of at least 5.3 mmol/L (95 mg/dL) fasting, 10.6 mmol/L (191 mg/dL) at one hour or 9.0 mmol/L (162 mg/dL) at two hours confirms it, as does 11.1 mmol/L (200 mg/dL) or more on the 50 g challenge test 2. With the one-step approach, the cut-offs are 5.1, 10.0 and 8.5 mmol/L (92, 180 and 153 mg/dL) 2, 11.
It usually goes away after delivery 8, but the risk of type 2 diabetes afterwards is almost 10 times higher than after a pregnancy without it 6. Diabetes Canada advises a 75 g OGTT 6 weeks to 6 months after birth, and the ADA advises testing every 1 to 3 years for life 2, 3.
Higher glucose goes with a larger baby and more delivery problems, and Cleveland Clinic also lists low blood sugar and breathing problems at birth 15, 12. Johns Hopkins Medicine notes it generally occurs too late in pregnancy to cause birth defects 9. Treatment lowers the risk of serious complications 4.
Not necessarily. Studies cited by the ADA suggest 70% to 85% of people diagnosed under one widely used set of criteria manage with eating and activity changes alone 3. If targets aren’t met, Diabetes Canada lists insulin or metformin, and the ADA prefers insulin first 2, 3.
Gestational diabetes care runs on fasting and after-meal numbers. Glyve keeps glucose, food, insulin, exercise, sleep and stress on one timeline, and the day view shades the target range you set from your care team’s plan. If you check with a meter, you can type each reading in by hand; a CGM is not required. If you wear one, Glyve reads glucose from Apple Health, or from Dexcom and FreeStyle Libre through your own Dexcom Share or LibreLinkUp follower account, where readings can arrive later than in the CGM’s own app. You can log a meal by typing, by voice or with a photo of the plate, a nutrition label or a barcode, and every estimate is a draft you check before saving. The week view shows whether a pattern repeats, and a PDF summary, CSV or AGP report lets you share the weeks with your care team when you choose. Glyve is not a medical device: it gives no medical advice, recommends no insulin doses and sends no glucose alarms.
How we write about diabetes. Spotted a mistake? Email info@glyve.ca and we’ll check it against the source.
Glyve keeps glucose, food, insulin, exercise, sleep and stress on one timeline.
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