Pregnancy · Risk screening
Gestational Diabetes Risk Calculator
A risk-factor check that tells you whether you need early gestational diabetes screening (at booking) or whether the standard 24-28 week test is enough. Plus what to expect at each step.
Last reviewed 28 May 2026
Gestational diabetes risk
Should I be screened early for gestational diabetes?
Tick every risk factor that applies. This is a triage tool — it tells you whether to ask for early screening, not whether you have GDM.
Select any risk factors that apply, or leave all unchecked to see the baseline pathway.
Risk band
Low
0 risk factors ticked
What does this mean?
No major risk factors selected. GDM risk is at population baseline (~5-10 % depending on country). Standard 24-28 week screening still applies — about half of GDM occurs in women without obvious risk factors, which is why universal screening is recommended.
Standard universal screening is appropriate
- •75 g oral glucose tolerance test (OGTT) between 24 and 28 weeks (one-step) — or the two-step glucose-challenge / 100 g OGTT pathway, depending on local protocol.
- •Maintain a balanced diet with consistent carbohydrate distribution across meals.
- •150 minutes a week of moderate activity (walking counts) supports glucose handling.
Do I need an early gestational diabetes test?
Tick every risk factor that applies to you in the calculator above. Three or more factors usually means an early screen at the booking visit; one or two means the standard 24-28 week test is enough. Either way, you can’t “opt out” of the universal 24-28 week screen — about a quarter of women diagnosed with GDM have no risk factors at all.
What is gestational diabetes — really?
Your placenta makes a bunch of hormones — placental lactogen, cortisol, oestrogen, progesterone — that increase as the pregnancy progresses. From around 20 weeks, these hormones make your body less responsive to insulin (the hormone that gets sugar out of your blood and into cells). Your pancreas normally pumps out 2-3 times the usual amount of insulin to keep up. When it can’t, your blood sugar runs high — and that’s gestational diabetes. About 7-14% of pregnancies are affected, varying by population.
What are the symptoms of gestational diabetes?
Honestly — usually none. That’s why we screen universally. Some women notice: more thirst than usual, peeing more often (hard to tell from pregnancy itself), more tiredness, recurrent thrush, sugar showing up on the dipstick at routine visits. Don’t wait for symptoms — the 24-28 week OGTT catches almost all cases.
What does the oral glucose tolerance test (OGTT) involve?
- Fast for 8-12 hours overnight (water only).
- Morning: blood drawn for a fasting glucose.
- Drink 75 g of glucose dissolved in water (very sweet, sometimes nauseating).
- Sit still for 2 hours — no eating, no walking around, only water.
- Second blood draw at 2 hours.
- Results usually back within 24-48 hours.
UK NICE NG3 diagnosis: fasting ≥ 5.6 mmol/L (101 mg/dL) OR 2-hour ≥ 7.8 mmol/L (140 mg/dL). US ACOG/ADA uses different thresholds (Carpenter-Coustan or IADPSG). Your local protocol is what counts.
Practical scenarios — should I worry?
Scenario 1: BMI 22, age 28, first baby, no family history
Zero risk factors. Standard 24-28 week OGTT is enough. No early screen needed. About 4% chance of GDM.
Scenario 2: BMI 32, age 38, family history (mum has type 2)
Three risk factors. Early screen at booking recommended — HbA1c or OGTT in the first trimester. If negative, the standard 24-28 week OGTT still happens.
Scenario 3: Previous GDM in last pregnancy
One high-impact risk factor. Recurrence rate around 40-50%. Early OGTT or fingerprick monitoring at booking is standard practice; 24-28 week OGTT also done if early screen is negative.
Scenario 4: South Asian heritage, BMI 27, otherwise healthy
NICE uses a lower BMI threshold (≥ 27) for South Asian women because GDM risk is higher at lower BMIs. You qualify for early screening on ethnicity-adjusted BMI alone.
Scenario 5: Polycystic ovary syndrome (PCOS), BMI 24, age 30
PCOS is a moderate risk factor (insulin resistance even outside pregnancy). One factor — standard 24-28 week screen, but discuss myo-inositol with your clinician (4 g/day; trial evidence of ~50% GDM risk reduction in PCOS, Pintaudi 2019).
What blood-sugar targets do I aim for if I have GDM?
- Fasting (first thing in the morning): under 5.3 mmol/L (95 mg/dL).
- 1 hour after a meal: under 7.8 mmol/L (140 mg/dL).
- 2 hours after a meal: under 6.4 mmol/L (115 mg/dL).
Most people are asked to check 4 times a day initially: fasting, plus 1-hour after breakfast, lunch, and dinner. Record in a diary. Bring it to your antenatal diabetes appointments.
What should I eat if I have gestational diabetes?
- 3 meals + 2-3 snacks daily. Never skip meals.
- Each meal: protein + non-starchy veg + a fist-size portion of low-GI carb. Examples: chicken stir-fry with brown basmati; lentil dahl with chapati and salad; eggs with wholegrain toast and avocado; fish with sweet potato and broccoli.
- Walk 10-15 min after each main meal — this drops 1-hour readings by 1-2 mmol/L.
- Limit fruit to 2-3 servings/day, preferably with meals, not alone.
- Cut out: sugary drinks, fruit juice, sweets / cakes / biscuits, white bread, white rice, sugary cereals.
- Carbs at breakfast are the trickiest — morning insulin resistance peaks. Go protein-heavy (eggs, Greek yogurt, beans) and small portions of carb.
- Plain sparkling water with lime = your new favourite drink.
Will I need metformin or insulin?
About 70-85% of women meet targets with diet + exercise alone (NICE figures). If after 1-2 weeks of diet/exercise your readings are above target on most days:
- Metformin tablets are usually offered first per NICE — start 500 mg with evening meal, build up to 2 g/day in divided doses. Convenient (tablet not injection) and safe.
- Insulin is added if metformin isn’t enough, or used first per ACOG preference, or used if there’s significant macrosomia. Several injection types depending on which time of day needs targeting.
- Both are safe in pregnancy. Neither causes birth defects.
- Around 50% of women who need medication need both metformin AND insulin by the end.
How will GDM affect my birth and baby?
- Well-controlled GDM: birth risks similar to background. Usually offered induction at 40+6 (NICE), earlier if on insulin.
- Macrosomia (big baby, ≥ 4 kg): raises caesarean rate, shoulder dystocia risk. Estimated weight ≥ 4.5 kg prompts a C-section discussion.
- Neonatal hypoglycaemia: baby’s pancreas adapts to your high sugar, then over-produces insulin after birth. Heel-prick glucose check at 2 hours; watched for 12-24 hours. Early breastfeeding helps.
- Jaundice and respiratory issues slightly more common, especially if delivered preterm.
- Long-term, the child’s risk of obesity / type 2 diabetes is modestly higher; reduced if you breastfeed and maintain a healthy weight afterwards.
Care guidance — the antenatal pathway with GDM
- Joint diabetes-antenatal clinic from diagnosis onwards (NHS pattern; private equivalents).
- Dietitian referral within 1 week of diagnosis.
- Self glucose monitoring 4×/day; review every 1-2 weeks initially.
- Extra growth scans at 28, 32, 36 weeks (more if concerns).
- Anaesthetic review if BMI high or birth plan complex.
- Birth plan discussion by 36 weeks — mode and timing.
- Baby’s heel-prick glucose at 2 hours; observed 12-24 hours.
- Postpartum OGTT or HbA1c at 6-13 weeks postpartum to confirm normal.
- Annual diabetes screening by your GP from then on — lifelong follow-up.
After birth — does GDM go away?
Yes for most women — sugars normalise within 24-48 hours of delivery as the placenta has gone. Insulin and metformin stop at delivery (unless you turn out to have pre-existing type 2 diabetes, which the postpartum test will pick up). Your lifetime type 2 diabetes risk is around 50% over the next 10-20 years without intervention — cut substantially by maintaining a healthy weight, breastfeeding, and 150 min/week of moderate exercise. ADA and NICE recommend annual diabetes screening after a GDM pregnancy.
Limitations of this tool
- This is a triage to advise on early screening, not a diagnosis. Only the OGTT (or, less commonly, an HbA1c ≥ 6.5% / 48 mmol/mol) diagnoses GDM.
- About 25% of women with GDM have no risk factors — the universal 24-28 week test catches them.
- Risk-factor weighting here is equal-weight; research models (Naylor, Teede equations) weight factors individually.
- Local protocols vary — ACOG, ADA, NICE, Australian guidelines agree on the broad approach but use slightly different cut-offs. Follow what your obstetric team uses.
- Educational only; doesn’t replace your antenatal team.
Sources
- American Diabetes Association. Management of Diabetes in Pregnancy: Standards of Care in Diabetes — 2024. Diabetes Care 2024;47(Suppl 1):S282-S294.
- ACOG. Practice Bulletin No. 230: Gestational Diabetes Mellitus. Obstet Gynecol 2018;131:e49-64.
- NICE. Diabetes in pregnancy: management from preconception to the postnatal period (NG3).
- HAPO Study Cooperative Research Group. Hyperglycemia and adverse pregnancy outcomes. N Engl J Med 2008;358:1991-2002.
- Stuebe AM, et al. Duration of lactation and incidence of type 2 diabetes. JAMA 2005;294:2601-10.
- Pintaudi B, et al. The effectiveness of myo-inositol and D-chiro-inositol on metabolic, hormonal and reproductive parameters in PCOS. 2019.
Frequently asked questions
What is gestational diabetes in plain English?
Gestational diabetes (GDM) is when your blood sugar runs too high in pregnancy, even though it was normal before. It starts because pregnancy hormones (mainly from the placenta) make your body less responsive to insulin from around 20 weeks. In most pregnancies your pancreas keeps up. In 7-14% (depending on your background), it can't, and your blood sugar rises. The good news: it usually goes away after birth, and treatment (diet, exercise, sometimes metformin or insulin) is very effective.
When am I tested for gestational diabetes?
Standard timing is 24-28 weeks. UK / NICE uses a 75g 2-hour oral glucose tolerance test (OGTT) — fasting plus a 2-hour blood sugar after drinking a sweet glucose drink. US standard is a two-step: 50g non-fasting glucose challenge first; if elevated, then 100g OGTT. If you have HIGH-risk factors, screening is done EARLIER — at the booking visit (8-12 weeks) — to catch undiagnosed type 2 diabetes that was there before pregnancy.
Who needs early gestational diabetes screening?
Earlier screening at booking (before 12 weeks) is recommended if you have: previous GDM, previous baby ≥ 4.5 kg (NICE) or ≥ 4 kg (some US criteria), BMI ≥ 30 (≥ 27 for South Asian women), first-degree relative with diabetes, glycosuria on dipstick, polycystic ovary syndrome, on long-term steroids, or two-or-more moderate risk factors. The early screen is usually HbA1c (≥ 5.7% / 39 mmol/mol suggests pre-existing type 2; ≥ 6.5% / 48 mmol/mol diagnoses it). If early screen is normal, the standard 24-28 week OGTT still happens.
What does the oral glucose tolerance test (OGTT) involve?
You fast for 8-12 hours (water only). You give a blood sample for fasting glucose. You drink 75 g of glucose dissolved in water (very sweet, sometimes nauseating). You sit still for 2 hours (no walking, no eating). At 2 hours you give a second blood sample. UK diagnosis (NICE NG3): fasting ≥ 5.6 mmol/L (101 mg/dL) OR 2-hour ≥ 7.8 mmol/L (140 mg/dL). Some test 1-hour readings too. Different countries use slightly different cut-offs — your local protocol is what counts.
Can I prevent gestational diabetes?
Risk can be reduced but not eliminated. The biggest lever is reaching a healthy pre-pregnancy weight — every 1 kg/m² of BMI above ~22 raises GDM risk roughly 4%. During pregnancy: 150 minutes/week of moderate exercise cuts GDM risk by about 30% (Cochrane 2015), balanced meals favouring low-glycaemic-load carbohydrates (wholegrains over white) help, adequate sleep matters, myo-inositol may help in PCOS (some evidence — 4 g/day). Mediterranean diet pattern in trials reduces GDM by ~20%.
What blood sugar levels are too high in pregnancy?
Once you're diagnosed with GDM and self-monitoring, the typical targets are: FASTING under 5.3 mmol/L (95 mg/dL); 1-HOUR POST-MEAL under 7.8 mmol/L (140 mg/dL); 2-HOUR POST-MEAL under 6.4 mmol/L (115 mg/dL). UK NICE uses fasting < 5.3, 1-hour < 7.8. ACOG / ADA similar. If you're consistently above target despite diet and exercise, your team will add metformin or insulin.
What can I eat if I have gestational diabetes?
Three meals + 2-3 snacks daily, never skipping. Each meal: a fist-size portion of low-GI carb (oats, basmati rice, wholegrain bread, sweet potato, beans, lentils), a palm-size protein (eggs, chicken, fish, tofu, paneer), and lots of non-starchy veg. Limit fruit to 2-3 servings/day, ideally with meals not alone. Cut out: white bread, white rice, sugary drinks, fruit juice, biscuits, cakes, sweetened cereals. Walk for 10-15 minutes after each main meal — drops your 1-hour reading by 1-2 mmol/L.
Will I need insulin or metformin?
Roughly 70-85% of women with GDM achieve targets with diet + exercise alone (NICE figures). If after 1-2 weeks your readings are above target on most days, your team will offer metformin tablets first (start 500 mg with evening meal, build up to max 2 g/day in divided doses). About 50% of women who need medication will need insulin too. Insulin is added if metformin isn't enough or if there's already significant macrosomia. Both are SAFE in pregnancy — metformin is the more convenient first option per NICE; ACOG slightly prefers insulin first.
How will gestational diabetes affect my baby?
If well-controlled, the risks are similar to background. If poorly controlled, the main risks are: macrosomia (large baby, ≥ 4 kg) which raises caesarean rate and shoulder dystocia risk; neonatal hypoglycaemia (baby's pancreas adapted to your high sugar, then has too much insulin after birth); jaundice; respiratory issues if delivered preterm; long-term, the child's risk of obesity / type 2 diabetes is slightly higher. Your baby will likely have a heel-prick glucose check at birth, watched for 12-24 hours, and you'll be encouraged to breastfeed early to keep their sugars stable.
When is my baby delivered if I have GDM?
Depends on control and other factors. Well-controlled GDM on diet alone: usually offered induction around 40+6 (not later than 41 weeks per NICE). GDM on metformin or insulin: offered induction by 39-40 weeks. Suspected macrosomia (baby ≥ 4 kg estimated): may be offered earlier. Caesarean is usually only on standard obstetric grounds — GDM alone doesn't mean a C-section, though estimated weight ≥ 4.5 kg often prompts that discussion.
Does gestational diabetes go away after birth?
Yes for most women. Glucose levels usually normalise within 24-48 hours of delivery as the placenta (which made the insulin-resistant hormones) is gone. Insulin / metformin is stopped at delivery. You'll have a 6-13 week postpartum oral glucose tolerance test or HbA1c to confirm normal. About 5-10% of women have type 2 diabetes that the pregnancy revealed (the test should pick this up). Going forward, your lifetime type 2 diabetes risk is around 50% over the next 10-20 years without lifestyle changes.
Will I get GDM again in my next pregnancy?
Recurrence rate is around 40-50%. Higher if: needed insulin/metformin last time, BMI rose since, age higher, weight retained after last birth, or earlier-onset GDM. Lifestyle changes between pregnancies (-2 to -5 kg, regular exercise) cut the recurrence rate significantly. Whichever way, next pregnancy you'll be offered EARLY GDM screening (booking visit OGTT or HbA1c).
Can I breastfeed if I had gestational diabetes?
Yes — and breastfeeding is HIGHLY recommended. It reduces YOUR future type 2 diabetes risk by ~50% if you breastfeed for over 3 months (Stuebe 2005). It reduces your child's future obesity / type 2 diabetes risk too. Early breastfeeding (within the first hour) helps the baby's blood sugar stabilise after birth and avoids the early hypoglycaemia episodes. Metformin is safe in breastfeeding; most insulin is also safe (it's too large to cross into milk in meaningful amounts).
Is gestational diabetes my fault?
No. GDM is driven mostly by genetics, your pre-pregnancy body composition (which itself has strong genetic and socioeconomic drivers), your ethnicity, and pregnancy hormones. You can't 'cause' GDM by eating sweets in pregnancy. You can REDUCE risk through pre-pregnancy weight, regular exercise, healthy diet — but plenty of women who do everything right still develop it. It's not a failure; it's a manageable condition.
What if I'm vegetarian or vegan with GDM?
Completely manageable. Focus on plant proteins (lentils, beans, chickpeas, tofu, paneer, tempeh, eggs/dairy if vegetarian) with every meal — they slow glucose absorption. Wholegrain carbs (steel-cut oats, brown basmati, wholegrain pita) instead of refined. Plenty of non-starchy veg. Healthy fats (avocado, nuts, seeds, olive oil) help slow absorption. Vegan B12 supplementation is essential. A registered dietitian referral (often available NHS) is worth asking for if available.
Can I do my own glucose monitoring at home?
Yes — your team provides a glucometer and lancets. You'll be asked to check 4 times a day initially: fasting (first thing in the morning before eating/drinking) plus 1-hour or 2-hour after each main meal. After 1-2 weeks of good control on diet, monitoring may be reduced. Record everything in a diary (paper or app). Bring it to your appointments. The diary is what determines whether you stay on diet alone or step up to metformin/insulin.
What's the difference between GDM, type 1 and type 2 diabetes in pregnancy?
GDM = new in this pregnancy, usually goes away after birth. Type 1 = autoimmune destruction of insulin-making cells, lifelong, was there before pregnancy, always needs insulin. Type 2 = insulin resistance + relative insulin deficiency, was there before pregnancy (sometimes only diagnosed during pregnancy because that's when blood sugar is checked), can need tablets and / or insulin. The care pathways differ: type 1 needs careful insulin adjustment through pregnancy; type 2 may need to swap tablets for insulin; GDM is usually the most straightforward.
How does this relate to other calculators on BumpBites?
Companion: /calculators/gdm-ogtt for the actual diagnostic OGTT interpretation; /calculators/preeclampsia-risk for the overlapping risk-factor screen (BMI, age, autoimmune); /calculators/pregnancy-bmi for the weight-driven side; /calculators/calorie-calculator for trimester nutrition targets; /calculators/insulin-pregnancy for the clinician-facing insulin dosing.