Gestational Diabetes


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. 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

Epidemiology and Aetiology

  • 2-4% of women get gestational diabetes
  • >35 years
  • Obesity (BMI > 30)
  • Note that women with BMI >27 should be given advice on weight loss if planning pregnancy
  • Smoking
  • Previous stillbirth
  • Previous ‘large’ baby (>4.5Kg)
  • Previous episode of gestational diabetes
  • FH of type II diabetes
  • More common in Asians, those from the middle east and Black Africans
  • 40% of women with GD have none of these risk factors!


During pregnancy, maternal insulin sensitivity is naturally reduced. This increases maternal blood glucose levels, in order to provide enough glucose for the fetus, particularly in the third trimester.
  • The hormone Human placental lactogen (aka Human Chorionic Somatomammotropin) is responsible for reduce insulin sensitivity. It also alters maternal fat metabolism, releasing fatty acids as an alternate energy source for the mother, freeing up glucose for the fetus.

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
  • The risk of baby’s problems is greatest when glycaemic control is poor around the time of conception.
  • Fetal macrosomia – this is basically a big baby! The excess maternal glucose the baby is exposed to results in the storage of more fat than normal. Definition – abdominal circumference >70th percentile.
  • The newborn may be hypoglycaemic, as they have been producing their own endogenous insulin during pregnancy to counteract they hyperglycaemia of the mother. This is usually self-limiting, but may require IV glucose.
  • Increased risk of shoulder dystocia during delivery
  • Increased risk of jaundice
  • Increased risk (2x) of congenital defects: congenital heart disease, respiratory distress syndrome, NTD’s. the risk of defects is inversely related to level of control of the gestational diabetes.
    • The risk of congenital defect is highest in type II diabetes, and lowest in type I. the risk in gestational diabetes is moderate.
  • Increased risk of type II diabetes in later life
  • Increased risk of obesity in childhood


Mother’s risks

  • Increased risks of tears


Increased risk of type II diabetes in the mother

  • 50% will develop type II within 15 years
  • 50% of those requiring insulin will develop type II within 5 years

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

  • All mothers shuld be offered caesarean or induced birth after 38 full weeks. Those with proven Macrosomia should be informed of the risks of vaginal birth.

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!


Screening – takes place of all pregnant women with known risk factors 24 and 28 weeks to check for gestational diabetes. This is either a fasting glucose test or a random glucose test. If these are positive or suspicious, diagnosis is confirmed with a glucose tolerance test.

  • In those with previous GD, the test may be performed at 16-18 weeks for early diagnosis.

OGTT – Oral glucose tolerance Test – NICE recommend 2 hour 75g OGTT

  • The day before the test the patient should eat and drink and exercise normally (no restrictions).
  • They should then fast for 8-14 hours overnight, and the test is performed the following day.
  • At the start of the test the patient drinks a glucose containing solution (usually 75g glucose).
  • Blood glucose is measured at the start of the test, and at various intervals afterwards.
  • Normal levels:
    • Fasting <6
    • 1 Hour <10
    • 2 Hours <7.8


Some classify gestation diabetes into two types:
  • Type A1 – abnormal OGTT, but normal glucose levels during fasting and two hours after meals
    • Can usually be controlled with diet and exercise
  • Type A2 – abnormal OGTT and high levels of glucose during fasting and 2 hours after meals
    • May require pharmacological intervention

Glucose results

Fasting Glucose
2 Hour glucose
<6 mmol/L
<7.8 mmol/L
Impaired fasting glucose
6 – 7 mmol/L
<7.8 mmol/L
Impaired glucose tolerance
<7 mmol/L
>7.8 mmol/L
>7 mmol/L
>11 mmol/L


Treatment reduces the risk of congenital defects, but does not 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, and control fat intake. But be careful because low fat diet is not recommended for pregnancy! It may be useful o use complex carbohydrates, that reduces 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 carb intake at breakfast.

  • GI – foods are given a rating from 1- 100, e.g. glucose (100) and spaghetti (41). Foods below 55 are considered low GI.
  • Salt – monitor salt intake
  • Fruit + Veg – at least 5 portion a day!
  • Oily fish, lean meat, and polyunsaturated fats are also recommended
For most (80-90%) patients, this is enough. If diet and exercise are unable to bring glucose levels under control within 2 weeks, consider:

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.

Treatment can usually be stopped after birth, as the insulin resistance returns to normal. There is usually a random glucose test (not OGTT) at the 6 week checkup, and if this is all clear, treatment can be stopped.

  • Some patients then go for regular screening for type II diabetes.

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.

  • If insulin is used during pregnancy, the dose is usually increased by 50%

Other oral agents

  • Only metformin can be used. No other oral treatments can be used during pregnancy. Consider insulin.
Glucose during labour
Should be monitored every hour, and kept between 4-7 mmol/L
  • Consider Insulin + dextrose infusion in those with type I, or poorly controlled diabetes.
After Birth
Feeding of the baby should be encouraged – t reduce risks of hypoglycaemia.
  • Breastfeeding – glibemclamide and metforim are safe to take whilst breastfeeding. Other oral agents should be avoided.

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

  • Advise to take 5mg folic acid supplements when planning to conceive and for the first 12 weeks of pregnancy
  • Risks include:
    • Birth defects mentioned above
    • Increased risk of miscarriage
    • Increased risk of stillbirth and neonatal death
  • Women with BMI >27 who are planning to become pregnant should be given advice on how to lose weight

Targets for control in pregnant diabetics:

  • Fasting glcusoe – 3.5 – 5.9
  • 1 hour post prandial <7.8

Investigations and screening

  • Fetal USS – four chamber view of heart and outflow tracts at 18-20 weeks
  • Routine monitoring of fetal wellbeing is not recommended, unless pregnancy continues past 39 weeks.

Control of diabetic complication risk factors

  • HypertensionACE-i and angiotensin-II antagonists should not be used in pregnancy! Use alternative treatments if planning a pregnancy or as soon as pregnancy is known. Use
    • Methydopa
    • Methynifedipine
  • Statins – should be discontinued if planning pregnancy or as soon as pregnancy is known
  • Retinopathy – up to 20% will experience some retinopathy during pregnancy
  • Nephropathy – may worsen during pregnancy, avoid pregnancy is severe (e.g. creatinine >100, urea >4.5).

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

  • As soon as pregnancy confirmed (if not screened for >12 months)
  • Perform at first ante-natal appointment
    • Perform at 16-20 weeks if previous result positive
    • Perform at 28 weeks if previous result negative
  • 20% of diabetic mothers will develop proliferative retinopathy during pregnancy

Renal screening

  • At first appointment – dipstick for protein, albumin, creatinine. Refer to nephrologist if creatinine >120, or protein >2g/day
  • Thromboprophylaxis should be given to all those with protein excretion >5g/day

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