Gestational diabetes

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Quick Overview

Gestational diabetes mellitus (GDM) affects 3-5% of pregnancies in the UK and increases risks of macrosomia, shoulder dystocia, neonatal hypoglycaemia, and future type 2 diabetes. NICE NG3 emphasises early identification through risk-based screening, tight glycaemic control, and individualised delivery planning to optimise maternal and fetal outcomes.

Core Facts & Concepts

📊 Diagnostic Criteria (75g OGTT at 24-28 weeks):

  • Fasting glucose ≥5.6 mmol/L OR
  • 2-hour glucose ≥7.8 mmol/L
  • Single abnormal value diagnostic (NICE NG3)

🚩 Risk Factors Requiring OGTT:

  • BMI >30 kg/m²
  • Previous GDM
  • Previous macrosomic baby (≥4.5 kg)
  • First-degree relative with diabetes
  • Ethnicity: South Asian, Black Caribbean, Middle Eastern
  • Previous stillbirth or neonatal death

🎯 Target Blood Glucose Ranges:

  • Fasting: <5.3 mmol/L
  • 1-hour post-meal: <7.8 mmol/L
  • 2-hour post-meal: <6.4 mmol/L

Figure 1: Glucose tolerance test showing elevated 2-hour glucose level diagnostic for gestational diabetes

💊 Treatment Escalation:

  1. Diet & lifestyle (trial for 1-2 weeks)
  2. Metformin (if targets not met)
  3. Insulin (if metformin inadequate or fasting ≥7 mmol/L)
  4. Glibenclamide (if metformin/insulin declined)

Problem-Solving Approach

Step 1: Risk Assessment

  • Identify risk factors at booking appointment
  • Offer early OGTT (16-18 weeks) if previous GDM; repeat at 24-28 weeks if normal

Step 2: Monitoring Protocol

  1. Self-monitor capillary glucose 4 times daily (fasting + 1-hour post-meals)
  2. Weekly review until targets met, then every 1-2 weeks
  3. HbA1c NOT recommended for monitoring GDM

Step 3: Treatment Decisions

  • Start metformin if targets not met after 1-2 weeks of diet modification
  • Add insulin if:
    • Metformin inadequate after dose optimisation
    • Fasting glucose ≥7 mmol/L at diagnosis
  • Consider immediate insulin if significant fetal macrosomia or polyhydramnios

🚩 Red Flags:

  • Fasting glucose ≥7 mmol/L (immediate pharmacotherapy)
  • Estimated fetal weight >75th centile (intensify treatment)
  • Pre-eclampsia developing (delivery planning)

⚠️ Warning: Do NOT use HbA1c for diagnosis or monitoring in pregnancy-rapid red cell turnover makes it unreliable

Analysis Framework

ParameterDiet-ControlledMedication-Required
Fetal surveillanceUltrasound at 36 weeksUltrasound every 4 weeks from 28-36 weeks
Delivery timingAwait spontaneous labour (≤40+6)Offer delivery at 37-38+6 weeks
Mode of deliveryVaginal (if no obstetric contraindications)Elective caesarean if EFW >4.5 kg
Postnatal OGTT6-week postnatal OGTT (75g)6-week postnatal OGTT (75g)

Fetal Surveillance Protocol:

  • Diet-controlled GDM: Single ultrasound at 36 weeks for growth/liquor
  • Medication-treated GDM: Serial scans every 4 weeks from 28 weeks
  • Umbilical artery Doppler NOT routinely indicated unless growth concerns

Visual Aid

Delivery Planning Table:

ScenarioTimingConsiderations
Diet-controlled, no complications40+6 weeks maximumAwait spontaneous labour
Medication-treated37-38+6 weeksIndividualise based on control/complications
EFW >4.5 kg38 weeksDiscuss elective caesarean section

Key Points Summary

Diagnosis: Single abnormal OGTT value (fasting ≥5.6 or 2-hour ≥7.8 mmol/L)

Targets: Fasting <5.3, 1-hour post-meal <7.8, 2-hour <6.4 mmol/L

Treatment ladder: Diet (1-2 weeks) → metformin → insulin (immediate if fasting ≥7)

Fetal surveillance: Diet-controlled = scan at 36 weeks; medication = 4-weekly from 28 weeks

Delivery timing: Diet-controlled ≤40+6; medication-treated 37-38+6 weeks

Postnatal: 6-week 75g OGTT mandatory; annual HbA1c thereafter (50% develop T2DM within 10 years)

Common pitfall: Using HbA1c for GDM diagnosis/monitoring-always use capillary glucose

📌 Remember: 5-7-4 Rule - Fasting <5.3, 1-hour <7.8, 2-hour <6.4 (think descending numbers)

Practice Questions: Gestational diabetes

Test your understanding with these related questions

A 37-year-old woman at 28 weeks gestation presents with sudden onset dyspnea and chest pain. She has a history of previous DVT. D-dimer is elevated. What is the most appropriate anticoagulant if PE is confirmed?

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Flashcards: Gestational diabetes

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The correct position for women who have a cord prolpase is _____

TAP TO REVEAL ANSWER

The correct position for women who have a cord prolpase is _____

on all fours, on knees and elbows

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