Overview

Gestational Diabetes Mellitus (GDM)

1. Topic Overview (Clinical Overview)

Summary

Gestational Diabetes Mellitus (GDM) is defined as carbohydrate intolerance of variable severity with onset or first recognition during pregnancy. It is a condition of insulin resistance driven by placental hormones, leading to hyperglycaemia in the mother and subsequent effects on the fetus. GDM resolves shortly after delivery in most cases, but it is a powerful marker of future metabolic disease, with 50% of women developing Type 2 Diabetes within 10 years if lifestyle modifications are not adopted.

Key Facts

Definition: Glucose intolerance first identified in pregnancy.
Prevalence: Affects 5-8% of all pregnancies (rising globally).
Pathophysiology: Placenta secretes Human Placental Lactogen (hPL) which causes insulin resistance.
Diagnosis: 75g OGTT at 24-28 weeks (Fasting ≥5.6 mmol/L or 2-Hour ≥7.8 mmol/L).
Treatment: Lifestyle first, then Metformin, then Insulin.
Key Risk: Macrosomia (Big baby) -> Shoulder Dystocia.
Post-natal: Resolves after delivery. 50% lifetime risk of T2DM.

Clinical Pearls

The "5, 6, 7, 8" Rule: Fasting 5.6, 2-Hour 7.8 are the NICE diagnostic thresholds.

Metformin is Safe: The MiG Trial confirmed Metformin is safe and effective in pregnancy.

It's a Stress Test: GDM unmasks a pre-existing metabolic vulnerability. Pregnancy is a "diabetogenic stress test".

Why This Matters Clinically

GDM affects nearly 1 in 10 pregnancies and its complications (Macrosomia, Shoulder Dystocia, Neonatal Hypoglycaemia) are almost entirely preventable with good glycaemic control. The diagnosis also offers a crucial "Window of Opportunity" for long-term prevention of Type 2 Diabetes in the mother.

2. Epidemiology

Incidence & Prevalence

Prevalence (UK): 5-8% of pregnancies.
Prevalence (Global): Up to 15-20% in high-risk populations (South Asia, Middle East).
Trend: Increasing (Mirrors the obesity and T2DM epidemic).

Demographics

Factor	Details
Age	Risk increases with maternal age (>5 years).
Ethnicity	2-4x higher in South Asian, Black Caribbean, Middle Eastern populations.
Parity	Higher in multiparous women.

Risk Factors (NICE Criteria for Screening)

Offer OGTT if any one of the following:

BMI >30 kg/m².
Previous Macrosomic Baby (>4.5 kg).
Previous GDM.
First-degree relative with Diabetes.
High-risk Ethnicity.

3. Pathophysiology

The Diabetogenic State of Pregnancy

Pregnancy is a natural "anti-insulin" state.

1. The Fetus Needs Glucose

The fetus is a "glucose parasite". It needs a constant supply.
To ensure this, the placenta secretes hormones that make the mother's cells resist insulin, ensuring glucose stays in the blood for delivery to the baby.

2. The Key Hormones (The Placental Axis)

Human Placental Lactogen (hPL): The main driver. Blocks insulin action on muscle and fat.
Placental GH: Contributes to insulin resistance.
Cortisol: Rises 3-fold in pregnancy.
Progesterone: Also anti-insulin.

3. The Pancreatic Response

A normal pancreas compensates by producing 2-3x more insulin.
GDM occurs when the mother's beta-cells cannot keep up with the demand.

Physiology: The Pederson Hypothesis

The link between maternal glucose and fetal outcomes.

Maternal Hyperglycaemia -> Glucose crosses placenta freely.
Fetal Hyperglycaemia -> Fetal pancreas senses it.
Fetal Hyperinsulinaemia -> Insulin is a potent growth factor.
Result: Macrosomia (Big baby), Organomegaly.
At Birth: The glucose supply is cut. Insulin remains. Neonatal Hypoglycaemia.

4. Clinical Presentation

Symptoms

Most women are ASYMPTOMATIC. GDM is diagnosed on screening, not symptoms.

Signs

Red Flags (During Pregnancy)

[!CAUTION] Urgent Referral if:

Polyhydramnios (Excess amniotic fluid) - Suggests very poor control.

Macrosomia on scan (Abdominal Circumference >90th centile).

Reduced Fetal Movements.

If Symptomatic

Polyuria, Polydipsia, Fatigue.

5. Clinical Examination

Antenatal Assessment

Blood Pressure: GDM is strongly associated with Pre-eclampsia.
Fundal Height: Larger than dates may indicate Macrosomia.
Urine Dipstick: Check for Proteinuria (Pre-eclampsia) and Glucosuria.

Fetal Assessment

Growth Scans: Serial ultrasounds to monitor fetal growth (28, 32, 36 weeks).
Doppler: If growth restriction suspected (less common in GDM).
CTG: Monitoring fetal wellbeing, especially >37 weeks.

6. Investigations

Screening & Diagnosis

Test	Population	Timing
75g OGTT	All women with 1+ Risk Factor.	24-28 weeks.
75g OGTT	Previous GDM.	At Booking AND 24-28 weeks.

Diagnostic Criteria (NICE NG3)

Time Point	Threshold
Fasting	≥ 5.6 mmol/L
2-Hour Post-Glucose	≥ 7.8 mmol/L
(Note: These are stricter than non-pregnant diabetes criteria. WHO/IADPSG use slightly different values.)

Baseline Investigations (On Diagnosis)

HbA1c (to exclude pre-existing diabetes if >48 mmol/mol).
Renal function (U&Es, eGFR).
Urinalysis for Proteinuria.

Self-Monitoring

Finger-prick Blood Glucose (SMBG): Fasting + 1-hour post-meal. QDS.
Targets: Fasting <5.3 mmol/L, 1-hour post-meal <7.8 mmol/L.

7. Management

Management Algorithm (NICE Pathway)

┌─────────────────────────────────────────────────────────────────────┐
│                    GDM DIAGNOSED ON OGTT                            │
├─────────────────────────────────────────────────────────────────────┤
│                                                                     │
│  CHECK: What is the Fasting Glucose at Diagnosis?                   │
│                                                                     │
│  ├── Fasting &lt; 7.0 mmol/L ───────────────────────────────────────   │
│  │       ↓                                                          │
│  │   STEP 1: Lifestyle (Diet & Exercise) for 1-2 weeks.             │
│  │       ↓                                                          │
│  │   IF targets not met:                                            │
│  │   STEP 2: Add Metformin (titrate to 2g/day).                     │
│  │       ↓                                                          │
│  │   IF still not met:                                              │
│  │   STEP 3: Add Insulin.                                           │
│  │                                                                  │
│  └── Fasting ≥ 7.0 mmol/L ───────────────────────────────────────   │
│          ↓                                                          │
│      ACTION: Start Insulin IMMEDIATELY.                             │
│      (Diet alone will fail. Metformin alone may be insufficient.)   │
│                                                                     │
│  └── Fasting 6.0-6.9 + Macrosomia on Scan ───────────────────────   │
│          ↓                                                          │
│      ACTION: Start Insulin IMMEDIATELY.                             │
│                                                                     │
├─────────────────────────────────────────────────────────────────────┤
│                    DELIVERY PLANNING                                │
├─────────────────────────────────────────────────────────────────────┤
│                                                                     │
│  ├── Well Controlled on DIET ALONE:                                 │
│  │       → Induce at 40+6 weeks.                                    │
│  │                                                                  │
│  ├── On Metformin or Insulin:                                       │
│  │       → Induce at 38-39 weeks (to prevent late stillbirth).      │
│  │                                                                  │
│  └── During Labour:                                                 │
│          → VRIII (Sliding Scale) only if sugars unstable.           │
│          → Usually OK on hourly monitoring alone.                   │
│                                                                     │
└─────────────────────────────────────────────────────────────────────┘

Step 1: Lifestyle Intervention

Diet: Low GI, moderate carbohydrate, avoid refined sugars. 3 small meals + 2-3 snacks.
Exercise: 30 mins walking daily after meals helps lower post-prandial glucose.
Ketone Avoidance: DO NOT embark on very low calorie diets. Some studies suggest ketones may harm fetal brain development.

Step 2: Metformin

First-line Drug: Safe and effective. Crosses placenta but no evidence of harm (MiG Trial).
Dose: Start 500mg OD with food, titrate to 500mg TDS or 850mg BD.
Side Effects: GI upset (nausea, diarrhoea).
Note: Some women fail Metformin – need insulin.

Pharmacology: Drug Safety in Pregnancy

Drug	Safety	Notes
Metformin	✅ Safe (Level 1b)	MiG Trial. Crosses placenta.
Insulin	✅ Safe	Does NOT cross placenta. Gold standard.
Glibenclamide	⚠️ Caution	Crosses placenta. Risk of neonatal hypoglycaemia. Second line only.
SGLT2i	❌ Contraindicated	No safety data.
GLP-1 RA	❌ Contraindicated	No safety data.

Step 3: Insulin

Indication: Fasting >7.0, OR Metformin failure, OR Macrosomia present.
Regimen: Basal +/- Bolus. Often BD Levemir or Lantus. Add Novorapid if post-prandials high.
Titration: Aggressive. Review every 3-7 days.

Delivery Planning

Diet-controlled: Await spontaneous labour or induce by 40+6.
On Medications: Offer induction at 38-39 weeks.
Intrapartum: Hourly glucose checks. VRIII if persistently >7-8.

Drill Down: Intrapartum Glucose Management

Labour is a Fasting State.

The Challenge: Woman is nil by mouth, but still needs glucose/insulin balance.
Target: Blood Glucose 4-7 mmol/L during labour.
Protocol:
1. If on Diet Alone: Hourly checks. Often stable.
2. If on Metformin/Insulin:
  - Stop long-acting insulin on admission.
  - Use VRIII (Variable Rate IV Insulin Infusion) if glucose >8.
  - Co-infuse 10% Dextrose to prevent hypos.
3. Post-Delivery: Stop VRIII immediately. Insulin resistance vanishes.
Baby at Birth: Early cord clamp. Check glucose at 2 hours.

Drill Down: Oral Glucose Tolerance Test (OGTT)

How to do it right.

Patient must be fasting (8-14 hours).
Take Fasting Blood Glucose.
Patient drinks 75g Glucose (dissolved in 250ml water).
Patient rests (no eating/drinking/smoking).
Take 2-Hour Blood Glucose.
Interpret using NICE thresholds.

Common Failure: Patient eats before test -> Invalid.

8. Complications

Fetal / Neonatal Complications

Complication	Mechanism	Management
Macrosomia (>kg)	Fetal Hyperinsulinaemia (Growth factor).	Serial growth scans. Early IOL.
Shoulder Dystocia	Big shoulders get stuck on pubic symphysis.	McRoberts Manoeuvre. Obstetric emergency.
Neonatal Hypoglycaemia	Glucose supply cut, Insulin high.	Early, frequent feeds. Check heel-prick glucose.
Polyhydramnios	Fetal polyuria (from hyperglycaemia).	Scan monitoring. Risk of preterm labour.
Stillbirth	Increased risk if uncontrolled GDM.	Tight control + surveillance prevents this.
RDS (Respiratory Distress)	Insulin delays lung surfactant maturation.	Corticosteroids if preterm delivery needed.

Maternal Complications

Pre-eclampsia: 2-4x increased risk.
Caesarean Section: Increased rate due to Macrosomia.
Future T2DM: 50% lifetime risk.

Drill Down: The GDM & Pre-Eclampsia Link

Two sides of the same metabolic coin.

Shared Risk Factors: Obesity, Insulin Resistance.
Mechanism: Hyperglycaemia causes oxidative stress and endothelial dysfunction.
Implication: Monitor BP closely. Low threshold for Pre-eclampsia screening (PIGF).

Special Populations: Multiple Pregnancy (Twins)

Risk: Higher incidence of GDM.
Challenge: More placenta = More hPL = More Resistance.
Management: As per singleton. Tends to need more insulin.

Drill Down: Shoulder Dystocia

The Obstetric Emergency.

Definition: Delivery of the head, but shoulders do not follow with normal traction.
Risk: Macrosomia, GDM, Obesity, Previous Dystocia.
Management (HELPERR Mnemonic):
1. Help - Call for help (Neonatal team).
2. Evaluate for Episiotomy.
3. Legs - McRoberts (Flex thighs onto abdomen).
4. Pressure - Suprapubic (NOT Fundal!).
5. Enter - Internal manoeuvres (Rubin II, Wood's Screw).
6. Remove Posterior Arm.
7. Roll - All Fours (Gaskin Manoeuvre).

9. Prognosis & Outcomes

Natural History

GDM resolves within hours of placental delivery in >95% of cases.
The hyperglycaemia is driven by the placenta. No placenta = no GDM.

Long-Term Maternal Outcomes

Outcome	Risk
T2DM	50% lifetime risk.
Recurrence of GDM	30-50% in future pregnancies.
Cardiovascular Disease	Increased risk.

Prevention of T2DM Post-Pregnancy

The "Window of Opportunity".

Lifestyle: Weight loss, healthy diet, exercise.
Breastfeeding: Protective. Reduces risk.
Annual Screening: Fasting glucose or HbA1c annually for life.

Socioeconomic Impact

Health Inequality: GDM rates are higher in deprived areas and minority ethnic groups.
Screening Access: Ensuring OGTT availability in all settings is a public health priority.
Cost: GDM-related complications (C-Section, NICU, T2DM development) are major NHS cost drivers.

Quality Assurance: Key Audit Standards (NICE QS109)

Standard	Target
Women with risk factors offered OGTT	100%
Women with GDM receive targets within 1 week	100%
Women with GDM have 6-week postnatal glucose test	>0%
Women with GDM offered annual T2DM screening	>0%

Drill Down: Post-Natal Protocol

The 48 hours after delivery.

Stop Medications: All GDM meds (Metformin/Insulin) stopped IMMEDIATELY upon delivery.
Neonatal Glucose Monitoring: Check baby's blood sugar at 2-4 hours post-feed. Monitor for 24 hours.
Maternal Glucose Check: Fasting glucose before discharge.
6-Week Follow-Up (CRITICAL):
- Fasting Glucose: To confirm GDM has resolved.
- If High: Diagnose Type 2 Diabetes or Impaired Fasting Glucose.
Lifelong Surveillance: Annual HbA1c.

Drill Down: Future Pregnancy After GDM

Planning the next one.

Pre-conception Counselling: Strongly recommended.
Weight Optimization: Losing 5-10% body weight significantly reduces recurrence risk.
Metformin Pre-conception?: Some evidence for women with BMI >35 (research ongoing).
Testing: Offer HbA1c or Fasting Glucose before next pregnancy to exclude overt T2DM.

Drill Down: Contraception After GDM

All Options Available: GDM itself is NOT a contraindication to any method.
If Progressing to T2DM: Avoid estrogen-containing options if vascular disease develops. UKMEC guidance applies.
Message: "Don't get pregnant again until you know you're not diabetic."

Drill Down: Distinguishing Pre-Existing from GDM

A common exam trap.

Feature	Pre-existing DM	Gestational DM
Timing of Diagnosis	<20 weeks or early pregnancy	24-28 weeks
HbA1c at Booking	>8 mmol/mol	Normal
Retinopathy	May be present	Absent
Congenital Malformations Risk	HIGH (Periconception hyperglycaemia)	LOW (Develops after organogenesis)
Post-natal Testing	Remains diabetic	Resolves

Drill Down: NICE vs IADPSG Criteria

Why the values differ.

Criteria	Fasting	2-Hour
NICE (UK)	≥5.6	≥7.8
IADPSG/WHO (International)	≥5.1	≥8.5

NICE: More specific. Fewer diagnoses. Treats fewer women.
IADPSG: More sensitive. More diagnoses. Based strictly on HAPO data.
UK Practice: Use NICE. Know the international exists.

Exam Scenarios (Common Vivas)

Scenario 1:

Stem: 28-week pregnant woman, BMI 32, previous baby 4.8kg. What test do you arrange?
Answer: 75g OGTT.

Scenario 2:

Stem: OGTT shows Fasting 6.1, 2-hour 8.2. What is the diagnosis and first management step?
Answer: GDM. Trial of diet and exercise for 1-2 weeks.

Scenario 3:

Stem: OGTT shows Fasting 7.4. What is the action?
Answer: Start Insulin IMMEDIATELY (Diet will fail).

Scenario 4:

Stem: Newborn of GDM mother is irritable and jittery at 3 hours. What is the diagnosis and action?
Answer: Neonatal Hypoglycaemia. Check heel-prick glucose. Feed urgently or IV dextrose if severe.

Scenario 5:

Stem: Woman attends 6-week postnatal check. How do you confirm GDM has resolved?
Answer: Fasting glucose. Should be <5.6 mmol/L.

10. Evidence & Guidelines

Key Guidelines

Guideline	Organisation	Year	Key Points
NG3: Diabetes in Pregnancy	NICE	2015 (Updated 2020)	Diagnostic thresholds (5.6/7.8). Metformin first line.
GDM Management	RCOG	2020	Risk-factor based screening. Induction timing.

Landmark Trials

1. MiG Trial (2008) - Metformin in Gestational Diabetes

Finding: Metformin is non-inferior to Insulin for glycaemic control and neonatal outcomes.
Impact: Established Metformin as safe and effective first-line oral agent.

2. HAPO Study (2008) - Hyperglycaemia and Adverse Pregnancy Outcome

Finding: Continuous, linear relationship between maternal glucose and adverse outcomes (Macrosomia, C-Section).
Impact: Led to stricter diagnostic thresholds (IADPSG criteria).

11. Patient/Layperson Explanation

What is Gestational Diabetes?

Gestational diabetes is a type of diabetes that happens during pregnancy. It means your blood sugar levels are higher than normal, but usually only while you are pregnant. It usually goes away after your baby is born.

Why does it happen?

Your placenta (the organ that feeds your baby) releases hormones that block your insulin from working properly. For most women, the body can make extra insulin to cope. But if it can't, your blood sugar rises.

How is it treated?

Healthy Eating: Avoiding sugary foods and eating regular, balanced meals.
Activity: Walking after meals helps lower blood sugar.
Medication: If diet isn't enough, you may need Metformin tablets or Insulin injections.

Will my baby be affected?

With good control, most babies are perfectly healthy. The main risk is your baby growing too large, which can make birth more difficult. After birth, your baby's blood sugar will be checked because it can dip low for a few hours.

Will I be diabetic forever?

No, gestational diabetes almost always disappears after your baby is born. However, it is a warning sign that you are at higher risk of developing Type 2 Diabetes later in life. Keeping a healthy weight and staying active is the best way to prevent this.

Key Counselling Points (For Clinicians)

"It's not your fault": GDM is caused by placental hormones, not something you ate.
Emphasise the excellent outcomes with good control.
Explain the transient nature (it goes away after delivery).
Discuss the 50% lifetime T2DM risk as a call to action, not a sentence.
Encourage lifelong healthy habits and annual screening.

When to Refer / Triage

Scenario	Urgency	Action
OGTT positive, well, Fasting <7.0	Routine	Refer to Joint Diabetes Antenatal Clinic within 1 week.
OGTT positive, Fasting ≥7.0	Urgent	Same-day Diabetes Specialist review for Insulin.
Macrosomia on scan	Urgent	Obstetric review. Consider IOL earlier.
Polyhydramnios	Urgent	Review for control. Consider weekly scans.
Reduced Fetal Movements	Immediate	CTG and Obstetric Assessment (Same day).
Neonatal Hypoglycaemia (Symptomatic)	Emergency	Paediatric review. IV Dextrose.

12. References

NICE Guideline [NG3]. Diabetes in pregnancy: management from preconception to the postnatal period. 2015 (Updated 2020). Link
Rowan JA, et al. Metformin versus insulin for the treatment of gestational diabetes (MiG Trial). N Engl J Med. 2008;358(19):2003-2015. PMID: 18463376
HAPO Study Cooperative Research Group. Hyperglycemia and adverse pregnancy outcomes. N Engl J Med. 2008;358(19):1991-2002. PMID: 18463375

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. It does not replace professional medical judgement. Clinical decisions should account for individual patient circumstances.

Summary

Key Facts

Definition: Glucose intolerance first identified in pregnancy.
Prevalence: Affects 5-8% of all pregnancies (rising globally).
Pathophysiology: Placenta secretes Human Placental Lactogen (hPL) which causes insulin resistance.
Diagnosis: 75g OGTT at 24-28 weeks (Fasting ≥5.6 mmol/L or 2-Hour ≥7.8 mmol/L).
Treatment: Lifestyle first, then Metformin, then Insulin.
Key Risk: Macrosomia (Big baby) -> Shoulder Dystocia.
Post-natal: Resolves after delivery. 50% lifetime risk of T2DM.

Clinical Pearls

The "5, 6, 7, 8" Rule: Fasting 5.6, 2-Hour 7.8 are the NICE diagnostic thresholds.

Metformin is Safe: The MiG Trial confirmed Metformin is safe and effective in pregnancy.

It's a Stress Test: GDM unmasks a pre-existing metabolic vulnerability. Pregnancy is a "diabetogenic stress test".

Why This Matters Clinically

Factor

Details

Age

Risk increases with maternal age (>5 years).

Ethnicity

2-4x higher in South Asian, Black Caribbean, Middle Eastern populations.

Parity

Higher in multiparous women.

Test

Population

Timing

75g OGTT

All women with 1+ Risk Factor.

24-28 weeks.

75g OGTT

Previous GDM.

At Booking AND 24-28 weeks.

Time Point

Threshold

Fasting

≥ 5.6 mmol/L

2-Hour Post-Glucose

≥ 7.8 mmol/L

(Note: These are stricter than non-pregnant diabetes criteria. WHO/IADPSG use slightly different values.)

┌─────────────────────────────────────────────────────────────────────┐ │ GDM DIAGNOSED ON OGTT │ ├─────────────────────────────────────────────────────────────────────┤ │ │ │ CHECK: What is the Fasting Glucose at Diagnosis? │ │ │ │ ├── Fasting < 7.0 mmol/L ─────────────────────────────────────── │ │ │ ↓ │ │ │ STEP 1: Lifestyle (Diet & Exercise) for 1-2 weeks. │ │ │ ↓ │ │ │ IF targets not met: │ │ │ STEP 2: Add Metformin (titrate to 2g/day). │ │ │ ↓ │ │ │ IF still not met: │ │ │ STEP 3: Add Insulin. │ │ │ │ │ └── Fasting ≥ 7.0 mmol/L ─────────────────────────────────────── │ │ ↓ │ │ ACTION: Start Insulin IMMEDIATELY. │ │ (Diet alone will fail. Metformin alone may be insufficient.) │ │ │ │ └── Fasting 6.0-6.9 + Macrosomia on Scan ─────────────────────── │ │ ↓ │ │ ACTION: Start Insulin IMMEDIATELY. │ │ │ ├─────────────────────────────────────────────────────────────────────┤ │ DELIVERY PLANNING │ ├─────────────────────────────────────────────────────────────────────┤ │ │ │ ├── Well Controlled on DIET ALONE: │ │ │ → Induce at 40+6 weeks. │ │ │ │ │ ├── On Metformin or Insulin: │ │ │ → Induce at 38-39 weeks (to prevent late stillbirth). │ │ │ │ │ └── During Labour: │ │ → VRIII (Sliding Scale) only if sugars unstable. │ │ → Usually OK on hourly monitoring alone. │ │ │ └─────────────────────────────────────────────────────────────────────┘

Drug

Safety

Notes

Metformin

✅ Safe (Level 1b)

MiG Trial. Crosses placenta.

Insulin

✅ Safe

Does NOT cross placenta. Gold standard.

Glibenclamide

⚠️ Caution

Crosses placenta. Risk of neonatal hypoglycaemia. Second line only.

SGLT2i

❌ Contraindicated

No safety data.

GLP-1 RA

❌ Contraindicated

No safety data.

Complication

Mechanism

Management

Macrosomia (>kg)

Fetal Hyperinsulinaemia (Growth factor).

Serial growth scans. Early IOL.

Shoulder Dystocia

Big shoulders get stuck on pubic symphysis.

McRoberts Manoeuvre. Obstetric emergency.

Neonatal Hypoglycaemia

Glucose supply cut, Insulin high.

Early, frequent feeds. Check heel-prick glucose.

Polyhydramnios

Fetal polyuria (from hyperglycaemia).

Scan monitoring. Risk of preterm labour.

Stillbirth

Increased risk if uncontrolled GDM.

Tight control + surveillance prevents this.

RDS (Respiratory Distress)

Insulin delays lung surfactant maturation.

Corticosteroids if preterm delivery needed.

Outcome

Risk

T2DM

50% lifetime risk.

Recurrence of GDM

30-50% in future pregnancies.

Cardiovascular Disease

Increased risk.

Standard

Target

Women with risk factors offered OGTT

100%

Women with GDM receive targets within 1 week

100%

Women with GDM have 6-week postnatal glucose test

>0%

Women with GDM offered annual T2DM screening

>0%

Feature

Pre-existing DM

Gestational DM

Timing of Diagnosis

<20 weeks or early pregnancy

24-28 weeks

HbA1c at Booking

>8 mmol/mol

Normal

Retinopathy

May be present

Absent

Congenital Malformations Risk

HIGH (Periconception hyperglycaemia)

LOW (Develops after organogenesis)

Post-natal Testing

Remains diabetic

Resolves

Criteria

Fasting

2-Hour

NICE (UK)

≥5.6

≥7.8

IADPSG/WHO (International)

≥5.1

≥8.5

Guideline

Organisation

Year

Key Points

NG3: Diabetes in Pregnancy

NICE

2015 (Updated 2020)

Diagnostic thresholds (5.6/7.8). Metformin first line.

GDM Management

RCOG

2020

Risk-factor based screening. Induction timing.

Scenario

Urgency

Action

OGTT positive, well, Fasting <7.0

Routine

Refer to Joint Diabetes Antenatal Clinic within 1 week.

OGTT positive, Fasting ≥7.0

Urgent

Same-day Diabetes Specialist review for Insulin.

Macrosomia on scan

Urgent

Obstetric review. Consider IOL earlier.

Polyhydramnios

Urgent

Review for control. Consider weekly scans.

Reduced Fetal Movements

Immediate

CTG and Obstetric Assessment (Same day).

Neonatal Hypoglycaemia (Symptomatic)

Emergency

Paediatric review. IV Dextrose.