Manage pre-existing and gestational diabetes across conception, antenatal surveillance, birth and postpartum care while preventing hypoglycaemia, ketoacidosis and avoidable fetal complications.
Diabetes known before conception and diabetes first detected in pregnancy share a need for careful glucose control, but their risk profiles differ. Hyperglycaemia during early embryonic development increases congenital-anomaly and miscarriage risk, making preconception planning particularly valuable in type 1 and type 2 diabetes. Later excess fetal glucose exposure promotes fetal insulin secretion and growth, while established maternal vascular disease can instead produce placental insufficiency and a small fetus.
Preconception care should include HbA1c, retinal and renal assessment, review of hypoglycaemia and a medicine plan. NICE advises aiming below 48 mmol/mol when achievable safely and strongly advises delaying conception when HbA1c exceeds 86 mmol/mol. Discuss this supportively and provide contraception if wanted. Give folic acid 5 mg daily until 12 weeks. Review statins, ACE inhibitors, ARBs and glucose-lowering drugs before pregnancy; insulin and selected metformin treatment are used through specialist planning rather than abruptly leaving diabetes untreated.
Type 1 diabetes causes absolute insulin deficiency, while type 2 diabetes combines resistance and impaired secretion; either may coexist with established vascular complications before conception.
Placental and maternal hormonal changes increase insulin demand, exposing insufficient pancreatic reserve in susceptible patients and producing hyperglycaemia first recognised during pregnancy.
Maternal hyperglycaemia during organ formation increases developmental risk, explaining why glucose optimisation before conception has benefits that later treatment cannot fully reproduce.
Glucose crosses the placenta and stimulates fetal insulin production, promoting tissue growth and predisposing to hypoglycaemia after the maternal glucose supply ends at birth.
Removal of the placenta reduces insulin-antagonistic hormonal effects, causing a rapid fall in insulin requirements that must be anticipated in the delivery plan.
Gestational diabetes is commonly found through risk-based testing rather than classic polyuria, thirst or weight loss.
Large size or excess fluid can suggest glucose-related fetal exposure, while maternal nephropathy may produce a smaller fetus instead.
Recurrent low readings, nocturnal symptoms or loss of warning signs indicate that the monitoring and treatment plan needs adjustment.
Ketosis can develop rapidly with infection, vomiting or interrupted insulin delivery, and normal-looking glucose should not end the assessment.
Marked early-pregnancy hyperglycaemia or a high booking HbA1c may reveal established type 2 diabetes rather than a purely late gestational process.
Pregnancy lowers the renal threshold for glucose, so urinary glucose can occur without diabetes; repeated or marked glycosuria nevertheless warrants appropriate testing.
Starvation from prolonged vomiting can cause ketosis, but a pregnant patient with diabetes needs urgent assessment for diabetic ketoacidosis and its precipitant.
Severe hypoglycaemia and ketoacidosis can threaten maternal and fetal life; infection, vomiting and insulin-delivery failure are preventable or treatable contributors.
Macrosomia, shoulder dystocia, operative birth, neonatal hypoglycaemia and stillbirth risk increase with poor control, while vascular disease can instead restrict fetal growth.
Gestational diabetes predicts future type 2 diabetes and recurrence in later pregnancies, creating a continuing need for glucose surveillance and prevention support.
The OGTT diagnostic threshold and the capillary treatment target are intentionally different and should not be substituted for one another.
Increased metabolic demand and reduced buffering capacity mean vomiting with interrupted insulin can become dangerous before glucose reaches a familiar non-pregnant level.
CGM and hybrid closed-loop systems can help type 1 diabetes management but require training, review and a safe backup insulin plan.
Normal postnatal glucose does not erase the increased lifetime diabetes risk after gestational diabetes, making annual testing and prevention support worthwhile.
Using HbA1c alone to screen for gestational diabetes at 24–28 weeks.
Applying the fasting OGTT cut-off as the daily treatment target and accepting persistent elevated fasting readings.
Stopping basal insulin in type 1 diabetes during vomiting because the patient is eating less.
Missing the postpartum insulin reduction and causing recurrent maternal hypoglycaemia.
Ordering a routine postpartum OGTT despite the NICE fasting-glucose pathway without a specific local or clinical reason.
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A 30-year-old at 27 weeks has newly diagnosed gestational diabetes with fasting plasma glucose 7.3 mmol/L. She has no ketones or acute illness. What treatment approach should be offered now?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 7 Sept 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes
The diagnostic and treatment thresholds serve different purposes. The fasting OGTT threshold is 5.6 mmol/L, whereas the subsequent fasting capillary treatment target is below 5.3 mmol/L. A one-hour post-meal reading is not interchangeable with the diagnostic two-hour OGTT sample. Teach patients when to test, how to record meals and medication, and whom to contact about repeated excursions. HbA1c can help identify previously unrecognised diabetes but is not a replacement for OGTT screening or day-to-day glucose profiles later in pregnancy.
Nutrition advice should be practical, culturally appropriate and designed to sustain pregnancy nutrition. Offer dietetic input, distribute carbohydrate sensibly and favour lower-glycaemic-index foods. Physical activity such as walking after meals can improve glucose handling when obstetrically appropriate. Needing medication is not evidence that the patient has failed: placental insulin resistance often rises as gestation advances. Review glucose patterns within a defined interval so that persistent fasting or post-meal elevation receives timely treatment.
Insulin is adjusted to fasting and meal-related patterns, prior regimen, gestation and hypoglycaemia risk; there is no single safe pregnancy-wide starting dose. Continue essential basal insulin in type 1 diabetes during illness, using a personalised sick-day and pump-failure plan. Metformin may be considered when benefits outweigh harm. Contemporary product pregnancy wording has changed, so distinguish NICE recommendations, the selected product's authorisation and the specific indication instead of repeating an outdated blanket licensing statement.
Plan birth and neonatal care jointly. NICE recommends birth at 37+0–38+6 weeks for uncomplicated pre-existing type 1 or type 2 diabetes, and no later than 40+6 for uncomplicated gestational diabetes, with earlier birth if maternal or fetal complications arise. During labour follow the agreed glucose and insulin plan; NICE specifies hourly glucose and a 4–7 mmol/L range. After placental delivery insulin resistance falls quickly, so pre-existing diabetes needs immediate dose reduction and close monitoring. Early neonatal feeding and glucose assessment reduce preventable harm.
Review renal function, dehydration, hypoxia and gastrointestinal tolerance; withhold during acute illness that increases lactic-acidosis risk and check the selected product's current pregnancy authorisation.
Prevent insulin omission, product confusion and hypoglycaemia; supplies and device training are essential, and renal impairment or postpartum changes can reduce requirements.
Starting late does not reverse prior exposure; maintain glucose optimisation and investigate possible vitamin B12 deficiency when clinically indicated.