Gestational diabetes

What is it?

Gestational diabetes (GDM) is high or unstable blood sugar first diagnosed during pregnancy that goes away after the baby is born. It is not to be confused with regular diabetes. It can also be called ‘carbohydrate intolerance’ of pregnancy. GDM occurs because the placenta produces hormones that interfere with the body’s ability to use insulin effectively. Insulin is like a key that unlocks the door of cells, letting them access sugars in the blood for energy. Insulin resistance reduces the amount of glucose that can get into the cell, letting cells starve while the blood outside contains an excess of sugar.


All pregnant women encounter some insulin resistance, and this condition ensures that the baby gets enough calories to grow and develop properly, but for women with Gestational Diabetes this gets out of balance. Most women are able to produce enough insulin to counter the impact of placental hormones. Gestational diabetes

occurs when a woman’s pancreas cannot produce enough insulin to compensate for the increased resistance during pregnancy. This peaks around the 24th – 28th week of pregnancy so it is usually tested for at this time.


Is GDM dangerous for me or my baby?

A mother with gestational diabetes usually feels well and healthy, though some may feel tired or sluggish. Women with GDM are more likely to develop Type 2 diabetes later in life, usually within ten years of their diagnosis in pregnancy. GDM has been poorly understood in the past, and new research is emerging all the time. Current research suggests that if a mother has uncontrolled gestational diabetes, this may result in:

  • A very large (“macrosomic”) baby, whose blood sugar might crash soon after birth
  • An increased risk of unexplained stillbirth (the overall risk is still very low)
  • The baby is at higher risk of developing Type 2 diabetes or becoming obese in the first five to ten years of life


Arguments IN FAVOUR of routine testing & treatment

  1. GDM testing and treatment may provide an opportunity to reduce birth size, thereby reduce the risk of birth trauma and the higher c/s rate associated with bigger babies (up to 30% of mothers with a positive GTT have babies weighing more than 8lb 12oz / 4000g). It is hoped that treatment of those identified as having GDM may also reduce the very small increased risk of death of the baby associated with a positive
  2. GDM treatment aims to decrease problems in the newborn such as the incidence of hypoglycaemia (low blood sugars) and jaundice, and to reduce the chance that the child develops obesity, high blood pressure, diabetes and other health
  3. GDM testing benefits women by identifying those at high risk of diabetes later in life; developing good health habits in pregnancy can provide life-long
  4. Approximately 50% of women with GDM do not have any known risk


Arguments AGAINST routine testing & treatment

NB: A lot of research about GDM has emerged since 2010. In general, maternity care providers are increasingly supportive of routine testing and treatment for GDM. Still, your midwives will support you in whatever decision you make.

  1. 70% of women who test positive will have babies weighing less than 8lb 12oz/4000g, even without treatment, and most ‘larger than average’ babies are born to mothers with a normal GDM test result. Treatment with diet, insulin and early induction, has not yet been shown to significantly reduce the size of larger babies (which itself is of dubious significance), shoulder dystocia, birth trauma or cesaerian rates.
  2. Current available evidence indicates that the relationship between glucose intolerance in pregnancy and poor outcomes for the baby is a continuous one, and no single cut-off can separate pregnant women into those at high risk and those with no risk at all. When insulin is truly needed and what levels of average blood glucose level are best remain controversial. The cut-offs aim to balance risks and benefits, but some women with GDM will be missed, and others will treat
  3. There is little agreement on treatment and so treatment protocols vary
  4. Most GDM can be treated with diet and exercise; most existing research is based around a “typical” Western/North American diet. Recommendations for dietary modifications may not be as easy to incorporate into a culturally specific or allergy-specific
  5. The test used to screen for the condition is not About 15% of women who are given the initial


screening test will screen ‘positive’, and of those, about 15% will be diagnosed with GDM. In 1999, obstetricians Barrett and Pitman stated that between 50 and 70% of the women, if retested, would have a negative result. Others have since made this claim.

  1. Many of the delivery practices sometimes used with GD patients (early induction, high rate of c-section, routine supplementation of the baby, admittance to the nursery for observation, delayed contact with mother for nursing, etc.) interfere with the establishment of breastfeeding, which is of huge public health significance.


What are the risk factors for gestational diabetes?

The following women are at increased risk of developing GDM in pregnancy:

  • Women older than 25 years
  • Women of Hispanic, African, First Nations, Inuit, Metis, South or East Asian, Hindu, Pacific Island, or Indigenous Australian ancestry
  • Pre-pregnant body mass index (BMI) > 27
  • Previous history of GDM or glucose intolerance
  • Family history of Type 2 diabetes in first degree relative (parent or sibling)
  • Previous infant over 4000g or previously unexplained stillbirth
  • Repeated glycosuria (sugar in urine), polyhydramnios or suspected macrosomia in this pregnancy
  • Remember that approximately 50% of women with GDM have no risk


Testing for Gestational Diabetes?

The current test for GDM has been recommended since September 2010. In this test, you fast for 8 hours (usually overnight – have a snack before going to sleep and go to the lab first thing in the morning). The lab will take a blood test before you have anything to eat. You will then be given a drink containing 75g of sugar, and your blood will be tested again 1 and 2 hours after drinking the drink. You need to stay at the lab at this time, without eating   or walking around. Bring a book or a laptop, and ask to lie down if you need to. Gestational diabetes is diagnosed if any of the three blood sugar measurements are higher than the cut-offs. If you have an allergy to orange food dye, contact the lab in advance to arrange for a dye-free version.


A screening test is also available in BC; this identifies women who are more or less likely to have gestational diabetes. For this test, you can arrive at the lab any time (you do not need to fast). You will be given a 50g sugar drink, and your blood will be tested after one hour. If your blood sugar is higher than the cut off for this test, the recommendation is to move on to the 2-hour, fasting, 75g test described above. The 50g test is faster, more convenient, and involves fewer blood draws, but it does not give as reliable a result.


What happens to me if I test positive?

With a positive diagnosis you are referred to the Diabetes Education Centre at Victoria General Hospital. At this clinic, you will review your diet with a dietician, and you will be taught how to test and record your blood sugar every day. You will have regular appointments at the Centre until your blood sugar levels are well-controlled. If diet and exercise are not sufficient to control your blood sugars, you may start insulin treatment. At this point an obstetrician will be involved in your care. Whatever your treatment plan, it will be continued through your labour and into the immediate postnatal period. Your baby’s blood sugars will also be tested about three times after the birth. This is in line with hospital protocol at VGH.


What is the community standard in Victoria?

Routine screening is common practice, regardless of a woman’s level of risk. Because the risk of GDM increases with age, some women test positive in a second or third pregnancy even though they have been negative before.


The choice is yours! Please do not hesitate to bring any questions or concerns you may have about this issue.