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Gestational Diabetes

27 Nov, 2023

Gestational Diabetes

By Dr Grant Saffer

Gestational Diabetes affects about 5% of pregnant women in Australia and is usually diagnosed at about 28 weeks.

So what is Gestational Diabetes?

Insulin is a hormone produced by the pancreas that enables the body to use sugar or ‘glucose’ as an energy source. In pregnancy, it is normal for the cells of the pregnant mother to become a bit resistant to insulin. This resistance is caused by hormones produced by the placenta and starts in the middle third of pregnancy and peaks in the last third. This is a natural mechanism in the pregnant body to make the mother use more of her fat as a fuel source, thereby making available more of her glucose and protein for her baby’s growth.

Gestational Diabetes therefore occurs when the mother’s pancreas is unable to make enough insulin to overcome this resistance, and the glucose in her body rises to higher levels. It is this chronically elevated glucose level that causes many problems for the mother and the baby.

How can it complicate a pregnancy?

Uncontrolled elevated glucose levels in pregnancy results in mild to severe consequences for not only the mother but especially her baby. If a woman already has unmanaged diabetes at conception or early in pregnancy, there is already a 2 to 3 fold increase in the chance of having a miscarriage. There is also a 3 to 4 fold increase in the rate of congenital abnormalities, such as heart abnormalities, spinabifida, abnormal development of the lower spine and limbs, and facial clefts.

Then there are a number of problems as the pregnancy advances. The baby has a higher chance of prematurity with all the consequences of a baby in a nursery needing oxygen, help with breathing, poor sugar control, and problems with jaundice.

We know that the mother’s elevated glucose level causes excess nutrients to be passed to the baby making the baby grow more than it should which is termed ‘macrosomia’. It is good to have a nice healthy baby, but too big makes it more difficult to be delivered. So the caesarean section rate is higher, and the mother has to have a major operation that could perhaps have been avoided and born vaginally, there may be increased risks of birth trauma to both the mother and her baby. Sometimes the placenta gets to its ‘used by date’ too soon and the baby doesn’t get enough nutrients and fails to grow adequately. This is called growth restriction and the baby may need to be born early.

Gestational Diabetes can also cause Preeclampsia or ‘high-blood pressure in pregnancy’, this condition alone impacts on foetal growth, and in the mother can have serious consequences if untreated, including fitting and stroke. Polyhydramnios where there is excess fluid in the sac is another condition. As the baby is floating in a large ‘swimming pool’, when labour does come it may be in an unusual position and so unable to be born vaginally. When the waters break, they gush out fast, and if the head is not low down ‘plugging the hole’ so to speak, the cord can be washed into the vagina and this is known as cord prolapse, an emergency situation, as the oxygen supply is interrupted to the baby with dire consequences.

Because of all the problems associated with GD, the mother will be seen more often during her pregnancy with extra ultrasounds and foetal monitoring particularly towards the end of her pregnancy to check the baby’s growth and well-being. If the sugar control is good and the baby is growing normally then the mother can possibly go up to a week past her expected delivery date. However sometimes the pregnancy may need to be induced earlier, often at 38 weeks, to ensure a safe outcome for the mother and baby.

If Gestational Diabetes is poorly controlled in pregnancy, it can affect long-term development and function of pancreatic and fat tissue in the child, continuing to adulthood. As a consequence these babies as adults have a higher chance of obesity and diabetes themselves at an earlier age. We call this the metabolic syndrome.

Are you at risk?

Inherently people have a genetic susceptibility to developing GD and there is not much you can do about your genes! So firstly, you know you are at increased risk if you belong to a high risk ethnic group. Other risk factors include a family history of diabetes, or Gestational Diabetes in parents or siblings, a personal history of gestational diabetes in a previous pregnancy, if the mother herself was born greater than 4.1kg in birth weight, or has had a baby herself weighing greater than 4.1kg.

And then there is weight, the most important avoidable risk factor. If a woman has a BMI greater than 30 before pregnancy, puts on excessive weight in her pregnancy, or has a history of significant weight gain in her life, or has put on excessive weight between pregnancies, she is at a significant increased risk of developing Gestational Diabetes.

Testing for and managing Gestational Diabetes

At around 26 to 30 weeks a test is done called a glucose tolerance test (GTT). While fasting the mother takes a blood test and then drinks a standard sugar drink and a second blood test is taken at 1 and 2 hours after the drink. Elevated glucose levels imply gestational diabetes. At this time it is so important for the mother to be given a full explanation and information, so that she can gain an understanding of the disease. She is then referred to a diabetic educator who will discuss dietary changes.

Limiting carbohydrate intake to less than 40% of total calories, and spreading the load through the day, will make a difference. So 3 small to moderate meals, and 3 or 4 snacks per day, is the goal, concentrating on unprocessed low GI foods that have slower absorption (more fruits, veggies and grains; less flour as in bread and pastries, and potatoes). The mother will check her blood sugar levels on waking and then 2 hours after breakfast, lunch and dinner. The vast majority of women will control their sugar levels adequately. Occasionally extra insulin is needed which is given as a single dose or as a number of injections throughout the day. Exercise can help too, a moderate exercise program is sufficient and smoking is absolutely not a good idea! The better the control, the better all the outcomes!

During pregnancy with good management, most of the problems related to gestational diabetes can be controlled and overcome, so the outlook is positive! But it is important for those who have had gestational diabetes, to appreciate the increased risk of diabetes later on in life, and to have a yearly check with their GP.

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