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What is gestational diabetes?

A woman with gestational diabetes prepares a healthy meal Gestational diabetes is a serious complication of pregnancy but thanks to modern technology – screening tests, intensive obstetric monitoring and a variety of insulins – you can minimise the risks to yourself and your baby.

You are normally screened for gestational diabetes between weeks 25 and 28 of your pregnancy, and if you are diagnosed with it, don’t be alarmed. You can manage diabetes in your pregnancy fairly easily, and the majority of the time it goes away when you give birth.

For mothers who have previously been diagnosed with gestational diabetes, or who may be at high perceived risk, screening should occur earlier – from 16 to 20 weeks. If you have Type 1 or Type 2 diabetes, pre-pregnancy planning can help to make sure your pregnancy goes well with no complications.

Gestational Diabetes Mellitus (GDM)

Gestational diabetes or Gestational Diabetes Mellitus (GDM) has been defined as “carbohydrate intolerance of varying severity first manifested or diagnosed in pregnancy”.

GDM occurs in roughly 5-10% of pregnancies, and appears as elevated blood glucose levels – this is what is screened around the 25th to 28th week of pregnancy.

Women at greater risk of gestational diabetes include:

  • Women over 30 years of age
  • Women with a family history of Type 2 diabetes
  • Women who are overweight/obese
  • Women who have previously had gestational diabetes during pregnancy
  • Women who have previously delivered a large baby (greater than 4kg)
  • Women who have had difficulty carrying a pregnancy to term
  • Women from certain ethnic groups including: Indigenous Australians; Torres Strait Islanders; South Asian (Indian, Sri Lankan); Middle Eastern; East Asian (Chinese, Vietnamese); African; Pacific Island (Polynesian/Melanesian); Indigenous American

Your health care provider will offer a gestational diabetes screening test as a part of routine antenatal testing. They will suggest a Glucose Challenge Test, which is a 1-hour, non-fasting screening test on measured glucose load, or the more thorough Oral Glucose Tolerance Test (OGTT). This is a 2-hour, fasting screening test on measured 75g glucose load. Gestational diabetes is diagnosed if fasting blood glucose is more than 5.5 mmol/L and/or 2-hour level is more than 8.0 mmol/L

These tests are important as gestational diabetes can be easily treated and managed once detected.

The risks of un-managed diabetes in pregnancy include:

  • Significantly increased risk of stillbirth
  • Excessive fetal growth (creating babies in excess of 4kg weight)
  • Complications and higher risk at time of birth
  • Developmental immaturity in fetus (including lungs, kidneys, other organs, increased risk of cleft palate)
  • Low blood glucose levels for baby immediately following birth

Causes of Gestational Diabetes

There may be a number of causes of gestational diabetes. It is characterised by elevated blood glucose levels, and may be associated with insufficient or poorly-timed insulin release, and/or insulin resistance during pregnancy.

Typically, your insulin demand may be up to 2-3 times higher during pregnancy than normal. A number of hormones needed to promote the growth of your baby (especially human placental lactogen and progesterone) are present in large amounts during pregnancy, and have an opposite action to insulin. If the action of human placental lactogen and progesterone exceeds your ability to produce sufficient insulin, the result will be elevated blood glucose levels.

If your insulin delivery is deficient or poorly-timed, or you are overweight/obese, then insulin resistance may result. Insulin resistance is when your body is not using the insulin that you are producing effectively. This makes your blood glucose levels rise.

When your pregnancy is over and your insulin demands return to normal, gestational diabetes usually disappears.

Consequences of Gestational Diabetes

Gestational diabetes can have short and long-term implications for both you and your baby.

As glucose crosses the placenta, your baby is exposed to your high glucose levels. The fetal pancreas is usually functioning by 18 weeks, so elevated blood glucose levels will stimulate the fetal pancreas to produce extra insulin. This makes your baby store excess glucose as glycogen and fat, making your baby to grow excessively large (macrosomic). Certain organs, especially the fetal lungs and kidneys, can remain under-developed or immature even though your baby looks like it will have a large birth weight.

Large babies can create complications in delivery at birth. Immature or under-developed babies are also high-risk for a number of complications. The requirement for early delivery of an macrosomic baby can further complicate pre-maturity problems. Your baby may also have difficulty in coping after it is born, as it goes from a high-glucose environment to a much lower glucose environment.

Treatment of Gestational Diabetes

Gestational diabetes can be effectively managed and treated when health professionals work closely in co-operation with family to:

  • Correct high blood glucose levels
  • Monitor fetal wellbeing and growth; and
  • Make appropriate decisions about timing and mode of delivery.

Correcting High Blood Glucose Levels

Your pregnancy will most likely have a good outcome if you maintain your blood glucose levels as close to normal as possible.

  • Home-based blood glucose monitoring is very important.
  • Obstetrician/physician/GP will establish target levels (typically less than 5.5 mmol/L before breakfast and less than 7.0 mmol/L at a time two hours after meals)

Healthy Eating Patterns

It is highly recommended to consult a dietitian for advice on healthy eating patterns, diet, and proper nutrition for both yourself and your baby.

Here are some tips to make healthy food choices for gestational diabetes:

  • Eat small amounts of nutritious foods more often than normal to try and minimise excessive swings in blood glucose levels.
  • Choose a variety of healthy, nutritious foods.
  • Include foods which are sources of calcium, iron, folate and other critical nutrients.
  • Limit fat intake – especially saturated fats. Choose monounsaturated fats (olive or canola oils).
  • Limit ‘energy-dense’ junk foods high in saturated fat, sugar, and salt.
  • Include moderate quantity of preferably low-GI carbohydrates with every meal (wholegrains, cereals, fruit, vegetables, pasta, rice).
  • Avoid all sugary cordials and soft drinks.

Physical Activity

Participation in moderate physical activity can be very important in helping to maintain blood glucose levels as close to normal as possible. Even a brisk, 45 minute walk four times per week, or similar equivalent level of exercise and physical exertion, can have beneficial effects in improving insulin sensitivity to lower your blood glucose levels.

Insulin sensitivity is the ability of your body to use available insulin. The benefit of physical activity in increasing the metabolic rate can last for up to 24-36 hours and it can also improve fitness and help prepare the mother for the birth of the baby.

Blood glucose monitoring and Insulin

Regular testing of blood glucose levels is essential so that treatment can be assessed and changed as necessary. Your doctor or diabetes educator will advise on target levels to aim for. Typical blood glucose target levels are less than 5.5 mmol/L before breakfast and less than 7.0 mmol/L at time two hours after meals.

In the event that diet and physical activity are not able to control blood glucose levels, or when fetal growth seems to be excessive, additional insulin may be required for you and your baby’s health.

Insulins must be delivered by sub-cutaneous injection, however modern insulins and syringes, or pen delivery systems are safe and simple to use. With an insulin pen, the correct dose is selected by dialing it up, the needle is inserted under the skin, and the insulin dose is injected. Most women with gestational diabetes who require insulin treatment can achieve good control with one to four insulin injections per day. Up to four injections per day may be required to achieve very tight blood glucose control in some cases.

Insulin delivery is a supplement to healthy eating plan and safe exercise, and should be used only if diet and exercise do not work. Insulin and blood glucose monitoring may be important right up to when you give birth.

Monitoring fetal wellbeing and growth

Untreated gestational diabetes is associated with an increased risk of stillbirth, therefore pregnancies complicated by gestational diabetes are still regarded as ‘high risk’. In order to minimise risks, women with gestational diabetes are more likely to need more intensive obstetric care, more tests, and may require more interventions like induction of labour, forceps delivery, and caesarean section than normal pregnancies.

One of the methods used to decrease the risk of excessively large babies and stillbirth is to deliver early, however this also has risks, especially prematurity, where the baby might not be fully developed. For these reasons, obstetricians often use tests in ‘high-risk’ pregnancies to ensure that the fetus is healthy, the placenta is functioning adequately, and the fetus is safe.

Common tests can include:

  • Cardiotocography (monitoring fetal heart rate, variability etc)
  • Ultrasound between 30 and 34 weeks in pregnancy

Appropriate timing and mode of delivery

Most of the time, if you control your gestational diabetes well, there is no indication for delivery prior to full term (40 weeks).

If you have poor blood glucose control or evidence of excessive fetal growth, there is some evidence that induction of labour at 38-39 weeks can reduce the risks of difficulty with delivery.

In some cases where the fetus seems very large (i.e. more than 4.5kg), elective caesarean section may be suggested to minimise potential complications at birth.

After delivery

In 98% of women, blood glucose levels return to normal immediately after birth. It is common to monitor the mother’s blood glucose levels for up to two days after delivery, and no monitoring after that if everything appears normal.

An oral glucose tolerance test (OGTT) is usually performed six weeks after the birth and will usually be normal. It is important for your long-term health that you follow-through to make sure that this test is performed in the hectic weeks following pregnancy.

Depending on the severity of the your gestational diabetes, one major concern after delivery is the risk of hypoglycaemia or low blood glucose of the baby. Blood glucose levels are usually closely monitored and in some cases, supplementary glucose may be required for the baby.

Major longitudinal studies in Australia and overseas have shown that mothers who develop gestational diabetes are at increased risk of developing Type 2 diabetes later in life. More recent studies have similarly shown that children from pregnancies where the mother had gestational diabetes are more likely to develop Type 2 diabetes in early adulthood than ‘normal’ pregnancies.

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