Gestational diabetes is a common medical complication of pregnancy (1-5). It is an important condition as failure to diagnose and treat gestational diabetes can lead to poor pregnancy outcomes, and in severe cases, fetal death in utero may occur. However, with accurate diagnosis and management, outcomes are excellent.
There have been some changes in the way gestational diabetes is diagnosed and managed.
1. The diagnosis of gestational diabetes has changed
The original diagnosis of gestational diabetes was developed nearly 50 years ago (3). In 2010 there was a recommendation by the International Diabetes and Pregnancy Study Groups that the diagnosis of gestational gestational diabetes should change (4,5). The recommendation arose from a study called HAPO (Hyperglycaemia and pregnancy outcomes)(5). The HAPO tidy correlated blood sugar levels in pregnancy with poor outcomes in mothers and babies and formulated new cut off values for blood sugar levels in pregnancy (4,5).
Six years later, not all countries and clinicians have adopted the new recommendations. However, our research suggests the new diagnostic criteria are associated with improved outcomes (6).
Gestational diabetes is diagnosed on a blood test performed between 24 and 30 weeks of pregnancy. The diagnostic test is called a glucose tolerance test and involves an overnight fast, followed by a fasting blood sugar test. Women then drink a measured amount of glucose syrup and 1 and 2 hours later have further blood sugar tests.
The new diagnostic criteria are (4):
fasting level greater than 5 mmol/l
1 hour sugar level greater than 10mmol/l
2 hour sugar level greater than or equal to 8.5mmol/l.
2. Importance of diet
The importance of diet in the management of gestational diabetes has never been clearer.
The majority of women who adopt a diabetic diet will require no additional treatment.
Many maternity units will refer women diagnosed with gestational diabetes to a dietician for advice on a diabetic diet. However, information is also widely available on the Internet, and in libraries and from diabetes associations.
Monitoring blood sugar levels in conjunction with diet is important as no two people respond to a food source in the same way.
As a clinician I have seen women eat the same meal and one will have a normal blood sugar level and the second an elevated level. Therefore it is important to monitor your sugar levels along with your diet to assess how your body responds to particular foods. This will help you identify safe foods and those you should avoid.
Blood sugar levels are monitored using a finger prick test. Machines to record the blood sugar level may be hired from chemists.
3. Medication for gestational diabetes
If medication is required (about 30% of women) then traditionally this would have been Insulin.
However, increasingly Metformin, an oral medication, is prescribed. There are good safety studies for Metformin.
Your specialist will advise whether Metformin, Insulin or a combination of the two is required.
4. Monitoring the pregnancy
Because gestational diabetes is associated with an increased risk of pregnancy complications, additional monitoring of the pregnancy is required. This is usually in the form of ultrasound examinations and fetal cardiotocograph tests (CTGs).
Ultrasound examinations are ordered to assess fetal growth and placental health. The pathology in gestational diabetes arises in the placenta. High blood sugar levels damage the delicate blood vessels in the placenta, causing sugar to flood across into the baby. The baby’s developing hormone system responds to the high sugar level by releasing growth factors. This causes abnormal growth of the baby which is detected on ultrasound as an increase in the abdominal circumference.
In more severe cases, the delicate placental blood vessels are so damaged that the placental circulation shuts down, and the baby ends up being starved of nutrients, and becomes growth restricted.
Medical staff will usually plot the developing baby’s growth on a chart to assess if the overall growth of the baby, and the relative growth of the head, abdomen and femur bones are in proportion.
The ultrasound examination will also inform medical staff about blood flow in the placenta and if growth is abnormal, will record the blood flow within the baby’s head. Blood flow readings are called doppler studies. The results of doppler studies can assist in guiding delivery management.
Cardiotocograph tests may also be ordered to monitor the well being of the developing baby. We are currently finalising a study to investigate the optimal strategy to use CTGs in pregnancy complicated by gestational diabetes. However, our preliminary results suggest the tests should be reserved for pregnancies where medication is required in addition to diet, or where other complications have been noted.
5. Timing of delivery
There is no agreed gestation at which women with gestational diabetes should deliver. However, many people now believe that if the pregnancy has been managed with diet alone, and blood sugar levels have been controlled, and the baby’s growth is normal, then the pregnancy can progress to term and normal birth without the need for intervention. However, many centres still offer delivery at 40 weeks.
If the pregnancy is complicated because medication was required in addition to diet, or the baby’s growth was abnormal, or a CTG was abnormal, then earlier delivery is required.
6. Follow up after delivery
All women who were diagnosed with gestational diabetes should have a follow up assessment within six months of delivery. This should involve a repeat glucose tolerance test. In our clinic, we also screen for thyroid and cholesterol abnormalities. We have found women with gestational diabetes have an elevated risk of developing type 2 diabetes, thyroid and cholesterol problems (7).
Sadly, many women fail to receive postnatal follow up and a valuable opportunity to improve their long term health through early diagnosis of chronic disease is wasted.
Gestational diabetes is easy to diagnose and manage. Most women will only require dietary changes, monitoring of blood sugar levels and some additional investigations.
It is important to screen and treat as otherwise pregnancy complications can harm mother and baby.
1. American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes care 2009; 32(S1): S62-S67.
2. Metzger BE, Coustan DR: The organizing committee. Summary and recommendations of the Fourth International Workshop-Conference on Gestational Diabetes Mellitus. Diabetes care 1998; 21(S2): B161-B167.
3. O’Sullivan JB, Mahan CM. Criteria for oral glucose tolerance test in pregnancy. Diabetes 1964;13: 278-285.
4. International Association of Diabetes and Pregnancy Study Groups Recommendations on the Diagnosis and Classification of Hyperglycemia in pregnancy. Diabetes Care 2010; 33: 676-682.
5. Metzger BE, Lowe LP, Dyer AR et al. The HAPO Study Cooperative Research Group. Hyperglycemia and Adverse pregnancy outcomes. N Engl J Med 2008; 358: 1991-2002.
6. Silbartie P, Quinlivan JA. Implementation of the International Association of Diabetes and Pregnancy Study Groups Criteria: Not Always a Cause for Concern. Journal of pregnancy 12/2015; 2015(2):1-5. DOI: 10.1155/2015/754085
7. Quinlivan JA, Lam D. Cholesterol abnormalities are common in women with prior gestational diabetes. J Diabetes Metab 2013; 4(4): 255. doi: 10.4172/2155-6156.10000255.
3 thoughts on “What’s new about gestational diabetes?”
Why don’t New Zealand use the new GDM criteria? They still seem to be using old ones with much higher cut off points.
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The NZ government are worried it will cost too much if they use the new diagnosis. Too many women would need care for GDM. They are running their own research instead.
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The diagnosis of GDM in NZ does not rely on the IADPGS criteria. I suggest pregnant women ask their maternity care provider about the results of their GTT and ask for individualised advice.
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