NICE vs RCOG: Management of Gestational Diabetes (2025)

This guideline provides a comparative analysis of the National Institute for Health and Care Excellence (NG3, updated 2025) and the Royal College of Obstetricians and Gynaecologists (Green-top Guideline No. 68, 2023) guidelines for the management of Gestational Diabetes Mellitus (GDM). It is designed to aid UK clinicians in understanding the nuances between these two key documents to inform clinical practice.

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Diagnosis and Assessment

The most significant divergence between NICE and RCOG lies in their diagnostic criteria, a difference rooted in the adoption of different international consensus thresholds.

NICE (NG3, 2025)

• Primary Test: 75g 2-hour oral glucose tolerance test (OGTT) at 24-28 weeks.
• Diagnostic Thresholds (venous plasma):
  • Fasting: ≥ 5.6 mmol/L
  • 2-hour: ≥ 7.8 mmol/L
• Risk Factors: NICE provides a list of risk factors (e.g., previous GDM, BMI ≥30, family history, certain ethnicities) to identify women for testing.

RCOG (GTG68, 2023)

• Primary Test: 75g 2-hour OGTT at 24-28 weeks.
• Diagnostic Thresholds (venous plasma): Uses the lower, more sensitive International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria.
  • Fasting: ≥ 5.1 mmol/L
  • 1-hour: ≥ 10.0 mmol/L
  • 2-hour: ≥ 8.5 mmol/L
• Risk Factors: Similar to NICE, but the lower threshold inherently captures a larger cohort.

Key Difference & Practical Takeaway: The RCOG criteria (IADPSG) will diagnose more women with GDM compared to NICE. The fasting threshold is the most common point of difference (5.1 mmol/L vs 5.6 mmol/L). Local hospital protocols typically adhere to one guideline, so clinicians must be aware of which standard their unit follows.

Treatment and Glycaemic Targets

Both guidelines advocate a stepped approach starting with diet and exercise, then escalating to pharmacotherapy if targets are not met.

Diet and Lifestyle

Both emphasise individualised dietary advice, carbohydrate management, and regular physical activity. Access to a specialist dietitian is crucial.

Pharmacological Therapy

• First-line: Both recommend metformin as the first-line pharmacological agent if lifestyle changes are insufficient.
• Second-line/Alternatives:
  • NICE: If metformin is contraindicated or not tolerated, the second-line option is insulin (e.g., isophane, soluble, rapid-acting analogues).
  • RCOG: Also prioritises insulin but provides more detailed guidance on the use of glibenclamide (a sulfonylurea), noting it may be considered but has a higher risk of neonatal hypoglycaemia and maternal weight gain compared to metformin and insulin.

Glycaemic Targets

• NICE:
  • Fasting: < 5.3 mmol/L
  • 1-hour postprandial: < 7.8 mmol/L
• RCOG:
  • Fasting: < 5.3 mmol/L
  • 1-hour postprandial: < 7.8 mmol/L or
  • 2-hour postprandial: < 6.4 mmol/L

Key Difference & Practical Takeaway: Treatment pathways are very similar. The key distinction is the RCOG's more cautious stance on glibenclamide and its provision of an alternative 2-hour postprandial target (6.4 mmol/L), offering flexibility in monitoring.

Special Situations

Postnatal Management and Follow-up

• NICE: Stresses that all women with GDM should have a fasting plasma glucose test at the 6-8 week postnatal check to exclude persisting diabetes. Advises annual HbA1c or fasting glucose testing thereafter for those with prediabetes, and lifelong lifestyle advice.
• RCOG: Largely concordant with NICE. Emphasises the importance of the postnatal OGTT (at 6-13 weeks) for all women to definitively classify glucose tolerance status (normal, prediabetes, or diabetes).

Timing and Mode of Birth

• Both guidelines agree that women with well-controlled GDM on diet alone should be offered induction of labour no earlier than 40+6 weeks.
• For women on medication (metformin/insulin), both recommend offering induction of labour between 38+0 and 39+6 weeks. Caesarean section should be offered only if estimated fetal weight is ≥4500g (in line with standard obstetric care).

Breastfeeding

Both strongly encourage breastfeeding. Metformin and insulin are considered safe during breastfeeding.

Practical Clinical Flow

A simplified, combined pathway reflecting common UK practice:

1. Identification: Assess risk factors at booking. Refer all high-risk women for an OGTT at 24-28 weeks.
2. Diagnosis: Perform OGTT using local protocol thresholds (NICE or RCOG).
3. Initial Management: Immediate referral to specialist multidisciplinary team (MDT). Commence diet and exercise advice, and provide a blood glucose meter for self-monitoring (fasting and postprandial).
4. Escalation: If glycaemic targets are not met after 1-2 weeks, commence metformin. Titrate dose as needed.
5. Second-line Therapy: If targets are not met with maximal metformin (or if contraindicated), add insulin. Consider glibenclamide only with caution and consultant approval (per RCOG).
6. Antenatal Monitoring: Increased fetal surveillance (growth scans) from 28-32 weeks. Discuss timing and mode of birth from 36 weeks.
7. Postnatal Care: Stop all GDM medication post-birth. Arrange postnatal glucose testing (fasting glucose or OGTT) at 6-13 weeks. Reinforce long-term health advice.

Frequently Asked Questions (FAQs)

1. Which guideline should I use in my practice?

This is determined by your local NHS Trust or Health Board. Most units will have a standard operating procedure (SOP) that adopts either NICE or RCOG criteria. It is essential to follow your local protocol to ensure consistency of care. NICE is often viewed as the national standard in England, but many centres use RCOG criteria.

2. Why are the diagnostic thresholds different?

The thresholds are based on different large-scale studies (HAPO study for IADPSG/RCOG) that correlated maternal glucose levels with adverse perinatal outcomes. The RCOG/IADPSG model prioritises sensitivity to prevent complications like macrosomia, while the NICE model aims for a balance between sensitivity and specificity.

3. Is one guideline "better" than the other?

There is ongoing debate. The RCOG approach may prevent more adverse outcomes by treating milder hyperglycaemia but increases the number of women labelled with GDM, with associated resource implications and potential for increased medicalisation of pregnancy. The NICE approach is more conservative. The clinical effectiveness of each strategy continues to be researched.

4. How should I manage a woman who meets RCOG but not NICE criteria?

If your unit follows NICE criteria, this woman would not be formally diagnosed with GDM. However, she has demonstrated glucose intolerance. It is prudent clinical practice to offer lifestyle advice, consider repeating the OGTT later in pregnancy (e.g., 32 weeks) if there is clinical concern (e.g., large-for-gestational-age fetus), and monitor fetal growth.

5. What is the key message for postnatal follow-up?

Do not discharge! GDM is a major risk factor for future Type 2 Diabetes. The 6-8 week postnatal glucose test is critical. Ensure it is performed and acted upon. Women with normal results should receive advice on weight management, diet, and exercise, and be advised of their elevated lifelong risk.

Source Links

• NICE Guideline NG3 (2025): Diabetes in pregnancy: management from preconception to the postnatal period
• RCOG Guideline GTG68 (2023): Gestational Diabetes