Dr Louise Johnson expands on what gestational diabetes is and if it increases the diabetes risk of your children.

What is gestational diabetes mellitus?

Gestational diabetes mellitus (GDM) is high blood glucose that develops during pregnancy and usually disappears after giving birth. It can happen at any stage of pregnancy but is more common in the second or third trimester.

This happens when your body can’t produce enough insulin to meet the needs in pregnancy. GDM can cause problems for you and your baby during pregnancy and after birth. thesanddollarlv The risks can be reduced if the condition is detected and well-managed.

Who is at risk for GDM?

Any woman can develop GDM during pregnancy, but you are at an increased risk if you:

• Have a body mass index (BMI) above 30. Normal is 18 to 24. This is calculated with the formula (BMI = kg/m2); kg is your weight in kilograms and m2 is your height in metres squared. Here is an example: weight of 70kg and length of 1.72 = 70/1.72 x 1.72 = 24.
• Previously had a baby who weighed 4.5kg or more at birth.
• You had GDM in a previous pregnancy.
• Have parents or siblings with diabetes.
• Are of Asian, black or Middle Eastern origin.

Symptoms of GDM

GDM doesn’t usually cause any symptoms. Most cases are discovered when your blood glucose is tested during pregnancy. This oral glucose tolerance test (OGTT) can be done at 24 weeks where you fast overnight and then consume 75g of glucose and blood tests are drawn before and two hours after the ingestion of the glucose. The test is positive when the fasting value is more than 5.3 mmol/L and two-hour glucose test more than 8.6 mmol/L.¹

Some women may develop symptoms of:

• Increased thirst
• Passing urine more often
• Dry mouth
• Tiredness

How GDM may affect your pregnancy

The following problems have been seen in GDM and aren’t well-controlled:

• Larger than usual baby (macrosomia) that leads to difficulties in delivery and possible caesarean section.
• Polyhydramnios (too much amniotic fluid in the womb). This can cause premature labour or problems at delivery.
• Premature birth (giving birth before 37 weeks of pregnancy).
• Pre-eclampsia, a condition that causes high blood pressure during pregnancy and can lead to pregnancy complications if not treated.
• Your baby can develop low blood glucose or yellowing of the skin and eyes (jaundice). This needs to be treated in hospital.
• The loss of your baby (stillbirth) although this is rare.
• Having GDM also means you’re at increased risk of developing Type 2 diabetes two to six years after the pregnancy.

Screening

During your first antenatal appointment at eight to 12 weeks of pregnancy, your doctor will ask questions to determine your risk for GDM. If you have one or more risk factors, you should be offered the OGTT screening test as described above. This test is done at 24 weeks of pregnancy.

Treatment

Problems during pregnancy can be reduced if your GDM is treated properly with the following management:

• Diabetic diet
• Light aerobic exercise like walking
• Metformin tablets
• Insulin injections
• Close monitoring of blood glucose before and two hour after meals and to keep levels between 4 and 6.6 mmol/L.

As pregnancy progresses, you may need more insulin injections but as soon as the baby is born the insulin can be stopped. It’s a good idea to stay on the metformin tablets to prevent the onset of Type 2 diabetes later in life.

Earlier than normal delivery of your baby is recommended if your blood glucose is not controlled, or your baby is growing too fast.

Long-term effects

Women who had GDM during a previous pregnancy are more likely to get it again with a next pregnancy. The risk of developing Type 2 diabetes two to six years after GDM is also increased. You should have a blood test to check for diabetes six to 13 weeks after giving birth and thereafter once a year if the test was normal.

To prevent developing Type 2 diabetes, healthy eating, normal weight and aerobic exercise (walking) is important.

Research suggests that babies from mothers who had GDM may be more likely to develop diabetes or become obese later in life.

Planning future pregnancies

If you had GDM with a previous pregnancy, check your blood glucose regularly and make sure it’s normal before falling pregnant again.

If you have diabetes, only fall pregnant once your blood glucose is well-controlled. The best test is the HbA1c that tests your average blood glucose the previous three months. A value of 6% or lower is good.

If the test before pregnancy is normal and the previous pregnancy you had GDM, screen for diabetes earlier in this pregnancy.

Remember that gestational diabetes can happen to any women during pregnancy. Healthy eating throughout pregnancy and light exercise is good advice. Don’t pick up too much weight and should you develop GDM follow all the rules and the outcome will be good.

Reference

1. NEJM 1999

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