Diabetes in Pregnancy

Pre-conception Care (Existing Diabetes)

• Aim for HbA1c <48 mmol/mol (6.5%) before conception
• Folic acid 5mg daily (from pre-conception until 12 weeks)
• Review medications: stop statins, ACE inhibitors, ARBs; switch to pregnancy-safe alternatives
• Retinal assessment before and during pregnancy (each trimester)
• Renal function assessment before pregnancy
• Advise on risks: congenital malformations (3-5x background), macrosomia, stillbirth, pre-eclampsia, neonatal hypoglycaemia
• Continuous glucose monitoring (CGM) recommended for type 1 diabetes in pregnancy

Gestational Diabetes (GDM)

Screening

• OGTT at 24-28 weeks if risk factors present:
  • BMI ≥30 kg/m2
  • Previous macrosomic baby (≥4.5 kg)
  • Previous GDM
  • First-degree relative with diabetes
  • Ethnicity with high GDM prevalence (South Asian, Black Caribbean, Middle Eastern)
• If previous GDM: offer OGTT at booking AND at 24-28 weeks if booking OGTT normal
• Self-monitoring of blood glucose as alternative to OGTT if OGTT not tolerated

Diagnostic Thresholds (NICE)

• Fasting glucose ≥5.6 mmol/L OR
• 2-hour glucose ≥7.8 mmol/L
• Note: IADPSG/WHO criteria use lower thresholds (fasting ≥5.1) — NICE deliberately chose higher thresholds based on cost-effectiveness analysis

Blood Glucose Targets in Pregnancy

| Timing | Target | |--------|--------| | Fasting | <5.3 mmol/L | | 1-hour post-meal | <7.8 mmol/L | | 2-hour post-meal | <6.4 mmol/L | | Pre-meal (Type 1) | 3.5-5.3 mmol/L | | Before bed (Type 1) | >4.0 mmol/L |

Management of GDM

Step 1: Diet and Exercise

• Dietary advice: balanced diet, regular meals, complex carbohydrates, avoid sugary foods
• 150 minutes moderate physical activity per week
• Trial for 1-2 weeks

Step 2: Metformin

• If fasting glucose <7.0 mmol/L and glucose targets not met with diet/exercise
• Start metformin 500mg with meals, titrate up
• Crosses placenta — no evidence of fetal harm in pregnancy; limited long-term offspring data
• Contraindicated if eGFR <30

Step 3: Insulin

• If glucose targets not met with metformin, or fasting glucose ≥7.0 mmol/L at diagnosis
• Rapid-acting insulin analogues (insulin aspart, lispro) are preferred for mealtime doses
• Isophane (NPH) insulin for basal cover
• Insulin dose requirements increase throughout pregnancy (insulin resistance peaks at 28-36 weeks)

Glibenclamide

• Consider if metformin not tolerated and patient declines insulin
• Not first-line — higher rates of neonatal hypoglycaemia and macrosomia compared to insulin

Fetal Monitoring

• USS at 28, 32, and 36 weeks for fetal growth (biometry + amniotic fluid)
• Assess for macrosomia and polyhydramnios
• Individual surveillance plan based on glycaemic control and complications

Timing and Mode of Delivery

• Pre-existing diabetes: offer elective delivery (induction or CS) between 37+0 and 38+6 weeks
• GDM (diet-controlled): avoid delivery >40+6 weeks; offer induction at 40+0-40+6
• GDM (on medication): offer elective delivery between 37+0 and 38+6 weeks
• Insulin-dependent: variable-rate IV insulin infusion (sliding scale) during labour; aim capillary glucose 4-7 mmol/L
• Caesarean section: consider if estimated fetal weight >4.5 kg (but ultrasound weight estimation has ±15% margin of error)

Neonatal Management

• Feed within 30 minutes of birth and every 2-3 hours
• Pre-feed blood glucose monitoring for at least 24 hours
• Neonatal hypoglycaemia: blood glucose <2.0 mmol/L requires intervention
• Other neonatal risks: polycythaemia, jaundice, respiratory distress, hypocalcaemia, hypomagnesaemia, cardiomyopathy

Postnatal Care

• GDM: stop all diabetic medication immediately after delivery
• Fasting glucose before discharge
• 6-13 week postnatal OGTT to exclude persistent diabetes (type 2 or impaired glucose tolerance)
• Annual HbA1c screening lifelong (GDM = 50% lifetime risk of type 2 diabetes)
• Lifestyle advice: weight management, diet, exercise to reduce long-term diabetes risk
• Pre-existing diabetes: reduce insulin dose immediately postpartum (insulin sensitivity returns rapidly); resume pre-pregnancy medications if not breastfeeding

Important Facts for MRCOG

• GDM diagnostic thresholds (NICE): fasting ≥5.6 OR 2-hour ≥7.8
• Management ladder: diet/exercise → metformin → insulin
• Folic acid 5mg for pre-existing diabetes
• Target fasting glucose <5.3 mmol/L, 1-hour post-meal <7.8 mmol/L
• Deliver between 37+0 and 38+6 for medicated GDM and pre-existing diabetes
• Sliding scale insulin in labour: aim glucose 4-7 mmol/L
• Postnatal OGTT at 6-13 weeks after GDM
• GDM = 50% lifetime risk of type 2 diabetes
• Metformin crosses placenta; insulin does not

Source: NICE NG3 (2020)

Read the original on nice.org.uk

Clinically reviewed by NHS obstetricians and gynaecologists · Source last updated 2020

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