Gestational Diabetes

Classification

• GDM
  • Glucose intolerance with onset or first recognition during pregnancy
  • Elevated plasma glucose levels less severe than overt diabetes
• Diabetes in pregnancy
  • Hyperglycaemia onset or first recognition during pregnancy
  • Plasma glucose levels exceed the threshold(s) for diagnosis of diabetes
    outside pregnancy
  • May indicate undiagnosed or pre-existing diabetes outside pregnancy, but
    a definitive diagnosis of non-gestational diabetes cannot be made until the
    postpartum period
  • Additional management (beyond that required for lower abnormal plasma
    glucose levels) is required
• Type 1
  • The body no longer makes its own insulin and cannot convert glucose into
    energy, resulting from β cell destruction that leads to near or absolute
    insulin deficiency
  • Commonly accompanied by autoimmune markers including anti-GAD,
    anti-IA-2A antibodies and anti-insulin antibodies
  • Daily insulin via injection or a continuous subcutaneous insulin infusion
    (CSII) pump is required
  • Diagnosis is usually established outside of pregnancy (before or after)
• Type 2
  • Hyperglycaemia resulting from insulin resistance and/or insufficient
    production of insulin
  • Lifestyle modification (diet and physical activity) is the cornerstone of
    management
  • Oral hypoglycaemic medication and/or insulin therapy is usually required
  • If woman is on non-insulin injectables (e.g. GLP1 agonists) these are
    ceased at pregnancy diagnosis, due to lack of safety data for use during
    pregnancy
  • Diagnosis is usually established outside of pregnancy (before or after) or
    may present as diabetes in pregnancy (confirm diagnosis postpartum)
  • Elevated HbA1c in first trimester
• Pre-diabetes
  • A condition in which blood glucose levels are higher than normal but not
    high enough to be diagnostic of diabetes
  • Includes impaired fasting glucose (IFG) and/or impaired glucose tolerance
    (IGT)
  • Diagnosis is established outside of pregnancy (before or after)

Diagnosis

• HbA1c (first trimester only)
  • ≥ 41 mmol/mol or 5.9%
    
• OGTT – 2 hour 75 g OGTT – one or more elevation of:
  • Fasting ≥ 5.1 mmol/L
  • 1 hour ≥ 10 mmol/L
  • 2 hour ≥ 8.5 mmol/L

Screening: 2nd Trimester – 24-28 weeks gestation

1. 2 hour 75 g OGTT
   • Maintain a normal diet
   • Fast for 8–14 hours before the OGTT
   • Drink water during fasting to prevent dehydration
   • Continue any usual medications
2. fasting BGL Glucose
   • OGTT not suitable/tolerated
   • If BGL 4.6–5 mmol/L, commence fasting and postprandial capillary BGL self monitoring for 1–2 weeks
     • Suggested targets:
       • Fasting < 5 mmol/L
       • 1 hour post prandial ≤ 7.4 mmol/L
       • 2 hours post prandial ≤ 6.7 mmol/L

Screening : 1st Trimester

1. 2 hour 75 g OGTT -OR-
2. HbA1c

if multiple RFs for early diagnosis:

• Ethnicity (ATSI, South Asian, Asian, African, Hispanic)
• Previous hx of GDM or glucose intolerance
• previous macrosomia (>4kg)
• Previous unexplained still birth
• Previous neonatal hypoglycaemia/ hyperbilirubinemia
• ↑ maternal age ≥ 35yrs
• Obesity
• repeated glucosuria in pregnancy
• polyhydramnios
• suspected macrosomia
• PCOS – If taking metformin for PCOS, OGTT results may be misleading
• acanthosis nigricans
• Corticosteroid use – Do not perform an OGTT within one week of steroids (betamethasone/dexamethasone) administration

if Bariatric Surgery

• If woman has had laparoscopic adjustable gastric banding (LAGB) or sleeve gastrectomy (SG)
  • Usual GDM testing may be possible
  • OGTT at 24–28 weeks gestation
  • If gastric band is tight or the woman is vomiting, OGTT unlikely to be tolerated
• If post malabsorptive Bariatric Surgery
  • (e.g. Roux-En-Y gastric bypass (RYGB), or biliopancreatic diversion)
  • an OGTT is not suitable due to altered gastric emptying including postprandial syndrome (“dumping syndrome”)

• In first trimester:
  • If history of diabetes or other risk factors
    • HbA1c > 48 mmol/mol (6.5%), or
    • fasting BGL is > 7.0 mmol/L
  • treating woman as if has type 2 diabetes
• In second trimester:
  • Fasting BGL between 24–28 weeks gestation
  • if BGL 4.6–5 mmol/L
    • recommend fasting and postprandial BGL for one to two weeks (selfmonitoring)

HbA1c vs GTT

• HbA1c is not suitable in pregnancy due to Physiological Changes in Pregnancy:
  • Dilutional anemia
  • reduced half-life of red blood cells
  • increased insulin resistance
• HbA1c does not provide real-time information about these fluctuations.

Risks from GDM

Maternal risks of GDM

1. Pre-eclampsia
2. ↑ rate of C/S delivery
3. Maternal birth injury
4. Gestational Diabetes Mellitus in future pregnancy 
5. PPH
6. Longterm risk of developing Diabetes Mellitus

Fetal/ neonatal risks of GDM

1. Macrosomia→ problems with delivery including shoulder dystocia and birth injuries including brachial plexus injury
2. Birth injuries
   1. Shoulder Dystocia or other Birth Trauma risk (RR 2.9)
3. Growth restriction
4. Respiratory distress
5. Hypoglycaemia
6. Jaundice
7. Hypoglycemia
8. Hypothermia
9. Hyperbilirubinemia
10. Hypocalcemia

Mx

• Tight glucose control – fasting BSL <5, postprandial <7
• Lifestyle management preferred
  • Based on principles of optimal nutrition and controlled weight gain
  • Effectiveness can be monitored by checking weight and BGL levels
  • Walking in everyday routine tends to be the most acceptable form of exercice
  • Patients should be advised to undertake 30 minutes of exercise (e.g. brisk walking) at least 4 times per week unless medically contraindicated

Medications

• Drugs contraindicated in pregnancy should be changed prior to conception. 
• These include; ACE inhibitors and A2 receptor blockers.
• Lipid lowering therapy must be ceased.
• Metformin
  • Safety and efficacy confirmed with long term effects to offspring being closely monitored but are to date reassuring
  • All other oral hypoglycaemic agents are contraindicated during pregnancy. Women with pre-existing diabetes treated with oral agents should ideally be commenced on insulin prior to conception if diabetes control is unsatisfactory.
• Insulin
  • Safe and effective
  • Basal bolus regime common
  • Insulin therapy will usually be basal-bolus with at least 1 dose of medium/long-acting insulin each day and short/rapid-acting insulin before each main meal or insulin pump
  • Encouragement of breastfeeding in the postpartum period has favourable  weight effects
• Education
  • Skills including sick day care. 
  • Hypoglycaemia management must be reviewed, including glucagon use by the partner. 
  • Suggestion for dealing with morning sickness could be discussed.

Follow-up

• All women with GDM should have follow-up OGTT at 6-12 weeks postpartum
• There is a 50% chance of a woman with GDM going on to develop T2DM in the  20 years subsequent

• All patients should perform home glucose monitoring at least 4 times each day before breakfast, and 2 hours after each meal
• The targets ≤5.0mol/L fasting and ≤ 6.7 mmol/L after meals
• Hb1c should be measured at the first visit and repeated monthly. The target level is <6.0%.