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Gestational Diabetes and Diabetes in Pregnancy

Dr Tom Leach
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Gestational Diabetes

Introduction

Resistance to insulin is a normal physiological response in pregnancy, thought to be induced by maternal hormones.  However, in some women, this is severe enough to result in gestational diabetes mellitus (GDM). In these women, there is reduced ability of the pancreas to produce enough insulin to overcome the insulin resistance.
Gestation diabetes is defined as – Any hyperglycaemia with first onset or presentation during pregnancy.
The incidence of gestational diabetes is increasing, in line with type 2 diabetes. It affects 2-10% of pregnancies (varies due to the criteria used) in developed countries such as the UK and Australia.
In most cases, it is asymptomatic and diagnosed on routine testing between 24-28 weeks.
The complications of gestational diabetes are similar to those of overt diabetes and include macrosomia (large baby for gestational age – which can cause problems in labour), neonatal hypoglycaemia and hyperbilirubinaemia. Treating GDM reduces these risks back to the baseline level of normal pregnancy.
Women with pre-existing type 1 or type 2 diabetes should be considered separately (see “Diabetes in Pregnancy” below) – and are usually referred to a endocrinologist or specialist diabetes in pregnancy service at the start of their pregnancy.

Epidemiology and Aetiology

Diagnosis

  • Guidelines are not always clear, or conflict, as to who to test and when
  • Most guidelines agree that an Oral Glucose Tolerance Test is the most useful diagnostic investigation, and that the best time to do this is between 24-28 weeks
  • NICE recommends testing any women with previous GDM at any stage of pregnancy (with OGTT), and repeating at 24-28 weeks if the first test is normal, AND women with any other risk factor be tested at 24-28 weeks
  • The Australasian Diabetes in Pregnancy Society recommends ALL pregnant women should be tested between 24-28 weeks, and women with any risk factors should have a random blood sugar level in their initial routine ante-natal blood tests
    • If BGL >7 – do OGTT
    • If BGL <7 or OGTT performed and is normal, repeat at 24 weeks
  • Interpreting the oral glucose tolerance test
    • 75g of glucose is given – usually in the form of a drink – to a fasted (>8 hours) patient. Usually the test is performed in the morning (e.g. 8 or 9am, with the patient fasted from midnight the night before)
    • Blood sugar readings are taken at 1 hour and 2 hours after the test
    • An abnormality in ANY of the below is enough to diagnosed gestational diabetes (note that different guidelines have different “abnormal” values – which is very confusing for medical students and also doctors practising in this field. The values given below are the “new” revised values from the Australasian Diabetes in Pregnancy Guidelines – I chose these because they are the most recent guideline that I came across):
      • Fasting >5.1 mmol/L
      • 1 hour post glucose >10.0 mmol/L
      • 2 hours post glucose >8.5 mmol/L
  • These testing regimens try to avoid a common pitfall of diagnosis – which is that glucose levels naturally rise in the third trimester, and thus relying purely on a glucose level, especially if only mildly elevated in the third trimester, may not necessarily indicate GDM
  • With these “new” cut-off values for diagnosis, the rate of GDM is expected to be about 12-14%. This is likely to have significant impacts on service provision

The role of HbA1c testing in gestational diabetes is still debated. It is recommended to check HbA1c in all women who are diagnosed with GDM – however, if the result is abnormally high this is usually an indicator or pre-existing Type 2 Diabetes, rather than an indicator or useful assessment of gestational diabetes.

All patients with GDM should have foetal USS every 4 weeks from 38 to 36 weeks to assess foetal growth and amniotic fluid volume.

Pathology

During pregnancy, maternal insulin sensitivity is naturally reduced. This increases maternal blood glucose levels, in order to provide enough glucose for the foetus, particularly in the third trimester. This means that mildly glucose levels in the third trimester should be interpreted with caution.

Clinical features and presentation

Diagnosis is not always very easy. It is often asymptomatic, and only discovered on screening. The common diabetic symptoms (thirst, hunger, polyuria, tiredness) are not particularly common, but are also seen in normal pregnancy in the third trimester anyway.
Baby’s risk with diabetic mother

 

Mother’s risks

 

Complications

Increased risk of type II diabetes in the mother

Increased risk of stillbirth – to reduce this risk, the many mother have a caesarean at 38-39 weeks (instead of the usual 40)

Increased risk of GD in subsequent births (30-85%) – particulary if pregnancy occurs within 1 year.
Type I diabetes – any women with type I diabetes who becomes unwell during pregnancy should have DKA excluded as a differential!

 

For the baby

Classification

Some classify gestational diabetes into two types:

Management

Evidence for the effectiveness of treatment is mixed. It is thought that treatment reduces the risk of congenital defects and labour complications, but does not necessarily reduce the risk of caesarean section or perinatal mortality.
Glucose levels should be monitored every 1-2 weeks during pregnancy
Similar to the normal management of type II diabetes: try diet and exercise modifications first, e.g.:

Exercise – low impact activities are encouraged – such as walking, swimming, yoga and pilates. Particularly important in those with BMI >27Kg. These women may also be instructed to restrict calorie intake.

Meals – eat regular meals, focus on the quantity and quality of carbohydrates and control fat intake. Aim for 175g of carbohydrates daily. Recommend use of complex carbohydrates, which reduce high peaks of glucose, and are digested slowly (“low GI foods”). Also, peak glucose levels are associated with breakfast more than with other meals, so it may be necessary to restrict carbohydrate intake at breakfast.

Advise patients to check blood sugar level daily at home:

For most (80-90%) patients, diet and exercise measures are enough. If diet and exercise are unable to bring glucose levels under control within 2 weeks, then medical interventions may be considered. Usually this is done with the support of an endocrinologist or a specialist diabetes in pregnancy service – and patients will require a referral from primary care to access these services.

Metformin +/- Insulin

Until 2008, it was recommended that type II diabetic mother considering pregnancy, and those with gestational diabetes should avoid oral medications, and go on to using insulin for the duration of the pregnancy. However a large study in Australia and NZ confirmed that oral treatments are as effective, and do not increase the risk of birth defects relative to insulin.

Metformin is thought to be particularly useful in obese women.

Indications for insulin

Rapid acting insulins (aspart and lispro) are more effective than endogenous insulins for controlling diabetes during pregnancy.
Insulin pumps should be recommended to those whose diabetes is not adequately controlled by multiple daily manual injections.

Other oral agents

Glucose during labour
Should be monitored every hour, and kept between 4-7 mmol/L

The time of birth

After Birth
Feeding of the baby should be encouraged – to reduce risks of hypoglycaemia in the newborn.

Treatment can usually be stopped after birth, as the insulin resistance returns to normal. NICE recommends a random glucose test at the 6 week checkup, and if this normal, treatment can be stopped. If this is not normal, then patients should undergo further investigation for T2DM – e.g. OGTT or HbA1c).

Follow-up

Diabetes in Pregnancy

Before pregnancy
Education of diabetic women of childbearing age from adolescence upwards is important. Tell them about the need to plan pregnancies so that they can unsure:

The diabetes is under control before pregnancy to give them the greatest chance of keeping it under control during pregnancy. Control should be measured with HbA1c test (should be below 6.1 for those planning on / who are pregnant. Those with HbA1c >10 should be strongly advised to avoid pregnancy!
The need to take folic acid supplements – 5mg/day when planning pregnancy and for 3 months after.
In type II diabetic mothers – Increased risk of birth defects

Targets for control in pregnant diabetics:

Investigations and screening

Control of diabetic complication risk factors

Antenatal care in diabetes

There is an increased level of care and surveillance for diabetic mothers. Typical measures, in addition to the normal antenatal care, may include:

Blood glucose monitoring – targets should be set, and reviewed every 2 weeks with a medical professional
Retinal digital screening

Renal screening

References

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