Gestational Diabetes

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | References

Definition

Gestational Diabetes Mellitus (GDM) is a condition characterised by glucose intolerance with onset or first recognition during pregnancy. It can lead to complications for both the mother and the fetus if not managed appropriately.

Aetiology

The exact cause of gestational diabetes is not fully understood, but it is thought to result from the hormonal changes of pregnancy that affect insulin action, leading to insulin resistance. Placental hormones, including human placental lactogen, growth hormone, and progesterone, play a significant role in this process.

Pathophysiology

During pregnancy, increased levels of hormones, including human placental lactogen, cortisol, and progesterone, contribute to insulin resistance. This physiological state is designed to ensure an adequate supply of glucose to the fetus. However, in some women, the compensatory increase in insulin production is insufficient to maintain normal blood glucose levels, resulting in gestational diabetes.

Risk Factors

• Previous history of gestational diabetes.
• Obesity (BMI ≥ 30 kg/m²).
• Previous macrosomic baby (birth weight ≥ 4.5 kg).
• Family history of diabetes (first-degree relative).
• Ethnicity: Higher risk in women of South Asian, Black, and Middle Eastern descent.
• Age ≥ 35 years.
• Polycystic ovary syndrome (PCOS).

Signs and Symptoms

Gestational diabetes is often asymptomatic and is usually detected through routine screening. However, in some cases, the following symptoms may be present:

• Increased thirst.
• Frequent urination.
• Fatigue.
• Blurred vision.
• Recurrent infections, such as thrush.

Investigations

• Oral Glucose Tolerance Test (OGTT): The gold standard for diagnosing gestational diabetes, typically performed at 24–28 weeks of gestation. A fasting glucose level is taken, followed by a 75 g glucose load, with glucose levels measured at 1 and 2 hours.
• Fasting Blood Glucose: May be used in some cases if OGTT is not available or as a preliminary test.
• HbA1c: Generally not recommended for diagnosing GDM but may be used to assess long-term glucose control if there is suspicion of pre-existing diabetes.
• Urine Testing: Urinalysis for glucose may indicate hyperglycaemia, but it is not diagnostic.

Management

• Lifestyle Modifications:
  • Diet: A healthy diet with controlled carbohydrate intake is the first-line treatment. Women are advised to eat regular meals with complex carbohydrates, fibre, and adequate protein.
  • Exercise: Regular moderate exercise, such as walking or swimming, is recommended to help control blood glucose levels.
  • Blood Glucose Monitoring: Women should monitor their blood glucose levels regularly, typically fasting and postprandial levels.
• Pharmacological Treatment:
  • Insulin Therapy: If blood glucose targets are not met with lifestyle modifications alone, insulin is the treatment of choice. Short-acting and long-acting insulins are used to control blood glucose levels throughout the day.
  • Metformin: May be considered as an alternative or adjunct to insulin in some cases, particularly if there is insulin resistance or difficulty with insulin therapy.
• Monitoring and Follow-Up:
  • Antenatal Monitoring: Regular monitoring of fetal growth and well-being is essential, including ultrasound assessments and non-stress tests if indicated.
  • Postpartum Care: Women with GDM should have a follow-up OGTT or fasting glucose test at 6–12 weeks postpartum to ensure glucose levels have returned to normal.
  • Long-Term Follow-Up: Women with a history of GDM are at increased risk of developing type 2 diabetes and should have regular follow-up and lifestyle counselling.

References

1. NHS (2024) Gestational Diabetes. Available at: https://www.nhs.uk/conditions/gestational-diabetes/ (Accessed: 24 June 2024).
2. National Institute for Health and Care Excellence (2024) Gestational Diabetes: Management. Available at: https://www.nice.org.uk/guidance/ng3 (Accessed: 24 June 2024).
3. Royal College of Obstetricians and Gynaecologists (2024) Green-top Guideline No. 36: Gestational Diabetes. Available at: https://www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg36/ (Accessed: 24 June 2024).
4. British Medical Journal (2024) Gestational Diabetes: Diagnosis and Management. Available at: https://www.bmj.com/content/350/bmj.h689 (Accessed: 24 June 2024).

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