What is gestational diabetes?
Diabetes (or significantly elevated blood glucose levels) during pregnancy are serious conditions but the risks to mothers and babies can be minimised and much better managed with early screening for diabetes, the availability of modern technologies, intensive obstetric monitoring and a variety of insulins.
The risks of "unmanaged 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
It is therefore important that all pregnant mothers participate in screening around the 25th to 28th week of pregnancy unless they are of known to be of higher risk when earlier consultation with obstetric team / diabetes management team at from 12-14 weeks is important.
For mothers with known Type 1 and Type 2 diabetes, pre-pregnancy planning may be necessary to enhance viability of normal births for babies.
Gestational Diabetes Mellitus (GDM)
Gestational diabetes or Gestational Diabetes Mellitus (GDM) has been defined as "carbohydrate intolerance of varying severity first manifest or diagnosed in pregnancy".
Estimated to occur in 5 to 10% of pregnancies, the condition is characterised by elevated blood glucose levels which should be screened in all pregnancies around the 24th to 28th week of pregnancy.
For mothers who have previously been diagnosed with gestational diabetes or may be at high perceived risk, screening should occur earlier from 16 to 20 weeks.
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
- Indigenous Australians and Torres Strait Islanders
- Women who have previously had gestational diabetes during pregnancy
- Women who have previously delivered a large baby (greater than 4000g)
- Women who have had difficulty carrying a pregnancy to term
- Women from certain ethnic groups:
- South Asian (Indian, Sri Lankan)
- Middle Eastern
- East Asian (Chinese, Vietnamese)
- Pacific Island (Polynesian/Melanesian)
- Indigenous American
It is imperative that all pregnant women undergo universal screening around 24th to 28th week of pregnancy which may include:
- Glucose Challenge Test (Initial Screening):
- 1-hour non-fasting screening test on measured glucose load
- May provide up 20% false negative results
- Oral Glucose Tolerance Test (OGTT) (More thorough test):
- 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
Causes of Gestational Diabetes
There may be a number of causes of gestational diabetes. Gestational diabetes, characterised by elevated blood glucose levels, may be associated with either or both insufficient or poorly-timed insulin release and/or insulin resistance during pregnancy.
Typically women's insulin demand may be up to 2-3 times higher during pregnancy than normal. A number of hormones needed to promote growth of fetus, (especially human placental lactogen and progesterone,) present in large amounts during pregnancy, have an opposite action to insulin. If the action of human placental lactogen and progesterone exceeds the mother's ability to produce sufficient insulin, the result will be elevated blood glucose levels.
If mother's insulin delivery is deficient or poorly-timed, or the mother is overweight / obese then insulin resistance may result. Insulin resistance is when your body is not using the insulin that you are producing effectively. The impact is that blood glucose levels will rise.
When pregnancy is over and insulin demands return to normal, gestational diabetes usually disappears.
Consequences of Gestational Diabetes
Gestational diabetes can have short and long-term implications for both mother and baby.
As glucose crosses the placenta, the baby is exposed to mother's 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 causes the fetus to store excess glucose as glycogen and fat, causing the baby to grow excessively large (macrosomic). Certain organs, especially the fetal lungs, kidneys can remain under-developed or immature even though a large birth weight baby is indicated.
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. Once the baby is born from a high-glucose environment, it may also experience difficulty in coping in a comparatively much lower blood glucose environment at birth.
Treatment of Gestational Diabetes
Gestational diabetes can be effectively managed and treated when health professionals work closely in cooperation 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
The pregnancy is most likely to have a good outcome if blood glucose levels are maintained 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 mother and baby, while making 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, folic acid 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 carbohydrate with every meal (wholegrains, cereals, fruit, vegetables, pasta, rice)
- Avoid all sugary cordials and soft drinks
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 walk of 45 minutes duration four times per week or similar equivalent level of exercise and physical exertion can have beneficial effects in improving insulin sensitivity to lower the mother's blood glucose levels. (Insulin sensitivity is the ability of your body to utilise 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
As previously mentioned, the 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 the health of both mother and baby.
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.
Again, insulin delivery is a supplement to healthy eating plan and participation in safe physical activity. Insulin and blood glucose monitoring may be important through until time of delivery.
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 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 it early, however this also has risks especially prematurity where some organs like lungs, kidneys and other organs are not 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
In most women with well controlled gestational diabetes, there is no indication for delivery prior to full term (40 weeks).
In women with 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 (ie more than 4500g) elective caesarean section may be suggested to minimise potential complications at birth. Of course caesarean section can be recommended on other obstetric grounds, not solely because of gestational diabetes.
Elevated glucose levels are resolved in 98% of women immediately after the birth of the baby. It is common to monitor the mother's blood glucose levels for up to two days after delivery and then to cease providing levels return to normal.
An oral glucose tolerance test (OGTT) is usually performed on the mother six weeks after the birth and will usually be normal. It is important for the mother's long-term health that she follows through to make sure that this test is performed in the hectic weeks following pregnancy.
Depending on the severity of the mother's 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.
Gestational diabetes is now very common in pregnancies affecting between 5-10% of pregnancies in Australia. Gestational diabetes is also potentially serious if unmanaged or untreated. With effective early screening, monitoring and modern management techniques the impacts of diabetes can be managed successfully so that this should be a happy time for families with positive outcomes for both babies and children.