Gestational Diabetes Mellitus ✅

🤰 Diabetes in Pregnancy includes pre-existing type 1 or type 2 diabetes and gestational diabetes mellitus (GDM). Blood glucose may fall early in pregnancy, but insulin resistance usually rises in the 2nd and 3rd trimester because of placental hormones 🌸. Good glycaemic control reduces maternal, fetal and neonatal complications 🩸.

📖 About

• Gestational diabetes is diabetes first diagnosed during pregnancy.
• Glycosuria is common in pregnancy because the renal glucose threshold is lower, so urine glucose alone is not diagnostic.
• Placental hormones, including human placental lactogen, progesterone and cortisol, increase insulin resistance in later pregnancy.
• Insulin requirements often rise in the 2nd and 3rd trimester.
• After delivery, insulin resistance falls rapidly once the placenta is delivered.

🧬 Pathophysiology

• Pregnancy is a state of progressive insulin resistance.
• In susceptible women, pancreatic ß-cells cannot produce enough extra insulin to overcome this resistance.
• This leads to maternal hyperglycaemia.
• Glucose crosses the placenta, but maternal insulin does not.
• The fetus responds by producing more insulin, which promotes growth and increases the risk of macrosomia and neonatal hypoglycaemia.

⚠️ Risk Factors for Gestational Diabetes

• BMI above 30 kg/m².
• Previous macrosomic baby weighing 4.5 kg or more.
• Previous gestational diabetes.
• First-degree relative with diabetes.
• Family origin with higher diabetes prevalence, including South Asian, Black Caribbean and Middle Eastern backgrounds.

🔎 NICE Diagnostic Criteria for Gestational Diabetes

NICE recommends diagnosing gestational diabetes using a 75 g 2-hour oral glucose tolerance test if either threshold is met.

🧪 Screening

• Screen women with risk factors using a 75 g 2-hour OGTT.
• For most high-risk women, offer OGTT at 24–28 weeks.
• If there was previous gestational diabetes, offer early self-monitoring of blood glucose or an early OGTT, then repeat testing at 24–28 weeks if early testing is normal.
• Do not rely on glycosuria alone to diagnose gestational diabetes.
• HbA1c may help identify pre-existing diabetes, but OGTT is used for NICE diagnosis of GDM.

🎯 Blood Glucose Targets in Pregnancy

Targets should be individualised and achieved without causing troublesome hypoglycaemia.

🛠️ Management

• Provide care through a multidisciplinary diabetes-in-pregnancy team.
• Give specialist dietary advice, including carbohydrate awareness and healthy eating.
• Encourage safe physical activity if appropriate.
• Teach regular capillary blood glucose monitoring.
• If glucose targets are not met with diet and exercise, consider metformin.
• If metformin is contraindicated, not tolerated or insufficient, offer insulin.
• Insulin may be needed immediately if glucose is very high at diagnosis or if there are complications such as suspected macrosomia or hydramnios.

💊 Medication

• Insulin: Safe and effective in pregnancy; used when targets are not met or hyperglycaemia is significant.
• Metformin: May be used in pregnancy when benefits outweigh potential harms.
• Other oral glucose-lowering drugs: Usually stopped in pre-existing diabetes and replaced with insulin, except metformin when appropriate.
• Pre-existing diabetes: Requires specialist review of medication, retinal status, renal function and pregnancy risks.

👁️ Monitoring for Pre-existing Diabetes

• Assess renal function and urinary albumin:creatinine ratio.
• Offer retinal assessment because diabetic retinopathy can worsen during pregnancy.
• Monitor blood pressure and urine protein because pre-eclampsia risk is increased.
• Use ultrasound surveillance to monitor fetal growth and amniotic fluid volume.

👶 Fetal and Obstetric Monitoring

• Offer serial ultrasound assessment of fetal growth and amniotic fluid volume.
• Assess for macrosomia and polyhydramnios.
• Discuss timing and mode of birth with the obstetric and diabetes team.
• Consider shoulder dystocia risk if fetal macrosomia is suspected.

⚠️ Risks of Diabetes in Pregnancy

• Maternal: Pre-eclampsia, operative delivery, worsening retinopathy in pre-existing diabetes, and future type 2 diabetes after GDM.
• Fetal: Macrosomia, polyhydramnios, shoulder dystocia, birth trauma and stillbirth risk if control is poor.
• Neonatal: Hypoglycaemia, respiratory distress, jaundice and admission to neonatal care.
• Pre-existing diabetes: Poor early glycaemic control increases risk of congenital malformations and miscarriage.

🏥 Labour and Birth

• Monitor capillary blood glucose regularly during labour.
• Aim to keep glucose usually between 4.0 and 7.0 mmol/L during labour and birth.
• Use local protocol for variable-rate IV insulin infusion if glucose is outside target or if clinically indicated.
• Neonatal team should be aware because babies are at risk of hypoglycaemia after birth.

🍼 After Birth

• Insulin requirements fall rapidly after delivery.
• Women with gestational diabetes can usually stop glucose-lowering treatment immediately after birth unless hyperglycaemia persists.
• Encourage breastfeeding where possible.
• Check for persistent diabetes after pregnancy.
• Give lifestyle advice because future type 2 diabetes risk is increased.

🔁 Postnatal Follow-Up After GDM

• Offer fasting plasma glucose testing 6–13 weeks after birth, or HbA1c after 13 weeks if fasting glucose was not done.
• Advise annual HbA1c testing thereafter to screen for type 2 diabetes.
• Advise weight management, healthy diet and physical activity.
• In future pregnancies, arrange early testing because recurrence risk is increased.

📚 Case Example

👩 A 32-year-old woman with BMI 34 kg/m² attends at 26 weeks. A 75 g OGTT shows fasting glucose 6.2 mmol/L and 2-hour glucose 9.8 mmol/L. ✅ Diagnosis: Gestational diabetes, because fasting glucose is ≥5.6 mmol/L and 2-hour glucose is ≥7.8 mmol/L. 🛠️ Management: Specialist dietetic advice, blood glucose monitoring, exercise advice if safe, and metformin or insulin if targets are not met. ⚠️ Delivery planning should consider fetal growth, macrosomia risk and neonatal hypoglycaemia risk.

🧠 Exam Pearls

• NICE GDM diagnosis: fasting glucose ≥5.6 mmol/L or 2-hour OGTT ≥7.8 mmol/L.
• Pregnancy glucose targets: fasting <5.3, 1-hour <7.8, 2-hour <6.4 mmol/L.
• Glucose crosses the placenta; insulin does not.
• Fetal hyperinsulinaemia causes macrosomia and neonatal hypoglycaemia.
• After delivery, insulin resistance falls quickly because the placenta has been delivered.

📚 Summary

Diabetes in pregnancy requires early recognition, careful glucose monitoring and multidisciplinary care. NICE diagnoses gestational diabetes using a 75 g OGTT with fasting glucose ≥5.6 mmol/L or 2-hour glucose ≥7.8 mmol/L. Good control reduces risks such as pre-eclampsia, macrosomia, shoulder dystocia and neonatal hypoglycaemia.