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Women's Health

Gestational diabetes

Gestational diabetes is pregnancy-related hyperglycaemia diagnosed by risk-factor-based OGTT when maternal insulin secretion cannot compensate for placental insulin resistance; treatment aims to reduce fetal overgrowth and neonatal hypoglycaemia while protecting maternal and fetal safety.

In a nutshell

Gestational diabetes is pregnancy-related hyperglycaemia caused by placental insulin resistance exceeding maternal beta-cell compensation. In NICE's risk-factor pathway, diagnose with a 75-g 2-hour OGTT, treat with diet and exercise then metformin or insulin according to glucose severity, and plan fetal, birth, neonatal and postnatal care as one pathway.

Classic presentation

Usually asymptomatic and detected by risk-factor-based OGTT; may present with glycosuria, fetal macrosomia or polyhydramnios.

Key points

  • NICE risk factors are BMI 30 kg/m² or more, previous macrosomic baby, previous gestational diabetes, first-degree family history of diabetes or ethnicity with high diabetes prevalence.
  • Use a 75-g 2-hour OGTT: diagnose with fasting plasma glucose 5.6 mmol/litre or above or 2-hour plasma glucose 7.8 mmol/litre or above.
  • Agree capillary targets: below 5.3 mmol/litre fasting, below 7.8 mmol/litre at 1 hour or below 6.4 mmol/litre at 2 hours, if achievable without problematic hypoglycaemia.
  • If fasting glucose at diagnosis is below 7.0 mmol/litre, trial diet and exercise; if targets are unmet after 1–2 weeks offer metformin, then insulin if needed or if metformin is unsuitable.
  • Fasting glucose 7.0 mmol/litre or above needs immediate insulin with or without metformin; 6.0–6.9 mmol/litre with macrosomia or hydramnios merits consideration of immediate insulin.
  • Advise birth no later than 40+6 weeks for gestational diabetes, monitor labour glucose, feed the baby early, check neonatal glucose and perform postnatal diabetes testing.

First-line investigation

Booking risk-factor assessment followed by a 75-g 2-hour OGTT at 24–28 weeks, or early self-monitoring/OGTT after previous gestational diabetes.

Management

Review and educate

  • Arrange joint diabetes and antenatal review within 1 week, explain risks and targets, provide self-monitoring education and give urgent advice for hyperglycaemia or illness.1,2

Start diet and exercise

  • Refer to a dietitian, provide individualised dietary advice and encourage safe regular activity while monitoring fasting and post-meal glucose against agreed pregnancy targets.1,2

Add metformin or insulin

  • Use the NICE fasting-glucose pathway: lifestyle trial below 7.0 mmol/litre, metformin if targets remain unmet after 1–2 weeks, insulin if metformin is unsuitable or inadequate, and immediate insulin for fasting glucose 7.0 mmol/litre or above.1,3

Monitor fetus and plan birth

  • Monitor fetal growth and amniotic fluid, assess maternal complications, discuss birth mode and advise birth by 40+6 weeks unless earlier birth is indicated by maternal or fetal complications.1,2

Protect mother and baby after birth

  • Monitor labour glucose, feed the baby early, check neonatal glucose, test maternal fasting glucose at 6–13 weeks and arrange annual HbA1c and future-pregnancy screening after a normal postnatal result.1,2,5

Exam traps

  • NICE does not use universal screening: offer OGTT because of risk factors, with early testing after previous gestational diabetes.
  • Do not diagnose gestational diabetes from HbA1c, random glucose or routine urine glucose; HbA1c at diagnosis helps identify pre-existing type 2 diabetes.
  • Fetal hyperinsulinaemia explains macrosomia and neonatal hypoglycaemia because glucose crosses the placenta but maternal insulin does not.
  • Do not wait 1–2 weeks for lifestyle treatment if fasting plasma glucose is 7.0 mmol/litre or above at diagnosis.
  • After birth, the mother's treatment often stops but future type 2 diabetes risk remains: arrange fasting glucose at 6–13 weeks and ongoing testing.

Illustrations

Placental hormones and maternal insulin resistanceDiagram showing human placental lactogen, progesterone and cortisol rising across gestation and antagonising maternal insulin action.PassFinals · original
The Pedersen hypothesisSchematic tracing maternal hyperglycaemia across the placenta to fetal hyperinsulinaemia, and onward to macrosomia and neonatal hypoglycaemia at birth.PassFinals · original
OGTT diagnostic pathwayFlowchart of risk-factor screening, the timing of the oral glucose tolerance test and the current fasting and 2-hour diagnostic thresholds.PassFinals · original

Key sources

  1. NICE NG3: Diabetes in pregnancy: management from preconception to the postnatal period (Current NICE guidance for gestational-diabetes risk assessment, OGTT diagnosis, glucose targets, diet and medication escalation, antenatal care, birth, neonatal care and postnatal testing; last reviewed 30 April 2025 with a February 2026 insulin-detemir supply note.)
  2. NHS: Gestational diabetes and treatment (Current NHS information on diagnosis, medicine escalation, monitoring, timing of birth, neonatal feeding and glucose checks, and postnatal testing; treatment page media reviewed May 2025.)
  3. BNF online: current diabetes medicines in pregnancy (Use the current BNF and local joint diabetes and antenatal protocol for metformin, insulin, hypoglycaemia prevention, ketone management and any medicine-supply changes; no fixed dose is reproduced here.)
  4. NICE NG229: Fetal monitoring in labour (Current NICE intrapartum fetal-monitoring guidance, including diabetes requiring medication as a higher-risk context for labour assessment.)
  5. NHS England: Diabetes Prevention Programme information for gestational diabetes (Current NHS England information on prevention support and future type 2 diabetes risk after gestational diabetes.)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.