Gestational Diabetes: Can we do better in the UK?
November 14 2008 was diabetes day!
This day of remembrance is meant to give the global community pause to celebrate what has been achieved in the biological basis, diagnosis and treatment of diabetes, as well as to collectively ask whether we can do better.
An area where we are not doing well in this country is the diagnosis and management of gestational diabetes mellitus (GDM). This is all the more relevant given the older ages of today’s expectant mothers, and that an increasing number had required extraordinary intervention to achieve their pregnancies.
Gestational diabetes refers to blood sugar abnormalities first uncovered during pregnancy.
The diagnosis must be made by a glucose tolerance test before week 32 of pregnancy. We recommend a GTT around week 26.
Normal pregnancy is an insulin resistant state. Recognising this, we have for several years recommended low glycaemic eating for all pregnant clients, with appropriate increases in carbohydrates as the pregnancy progresses, and with stress on weight control (and exercise and stress reduction) well into the second trimester.
Why is it important that gestational diabetes be diagnosed at an appropriate time?
Babies of women with gestational diabetes may have a number of medical problems at birth including:Baby
- excessive foetal growth (large babies),
- increased likelihood of birth trauma,
- increased rates of Caesarean section,
- neonatal jaundice requiring phototherapy
- hypoglycaemia and
- polycytheamia (thick blood), to mention the main ones.
Mum
- Increased risk for pre-eclampsia
- Post-natal depression
- Post-natal anxiety
A US task force on the subject has recommended that all pregnant women should be screened for gestational diabetes, with the object of intervening proactively in those who satisfy the criteria. No such recommendation exists in the UK (and many other European countries), and that includes women at special such as those with PCOS, strong family history of type 2 diabetes and ethnic groups with a high prevalence of insulin resistance and diabetes.
The World Health Organization (WHO) definition of GDM is "fasting blood sugar of equals or greater than 6.1mmol/l and a rise to 7.8 mmol /l or more after a 75 gram load of glucose". In a non-pregnant woman these criteria define those who are “Glucose Intolerant“ but not diabetic (peak glucose of 11.1 mmol/l or greater). The British Diabetic Association endorses the WHO definition. However, we at the London Endocrine Clinic have adopted the American Diabetes Association (ADA) criteria instead. This does not require a given fasting blood sugar to justify a Glucose Tolerance Test (GTT) before week 32 of pregnancy, with a peak cut-off of 7.8 mmol/l.
But are these conventional criteria enough to minimise adverse effects on babies?
As early as 1995, a collaborative study at the Metropolitan Toronto Hospital suggested increased adverse effects in women who did not satisfy the criteria of GDM but whose blood sugars were higher than normal in a GTT, a finding subsequently confirmed by others.
A recent Australian study this year suggests a lower threshold than is conventional may warrant medical intervention.
The Hyperglycaemia and Adverse Pregnancy Outcome (HAPO) studied the outcome of pregnancy in 23,000 using the same most of whom would not the WHO criteria i.e. with peak blood sugars in the GTT less than 7.8 mmol/l. The HAPO authors showed that there was a continuum in adverse events in proportion to the 60 minute and 120 minute glucose levels. The outcomes monitored included birth weight, neonatal hypoglycaemia, surrogate measures of insulin the cord blood as well as rates of Caesarean section. There was only a moderate increase (7-10%) in the rate in Caesarean sections in the women with higher sugars. The HAPO trial showed that women with higher blood sugar levels had higher rates of large babies but lower rates of babies small for gestational age.
An earlier Australian study asked whether medical intervention (diet, blood sugar monitoring by the patient and insulin therapy as necessary) would change outcomes in the babies of women whose peak blood sugar in a GTT was between 7.8 and 11.1 mmol/l. The Australian Carbohydrate Intolerance Study in Pregnant Women (ACHOIS) demonstrated improvement in outcomes in the intervention group (480) compared to the group receiving routine care (510). In essence they needed to treat 43 women to avoid an adverse event, a moderate gain for both baby and mother. To put this into perspective, clinical trials have shown that treating100 patients with Atrvostatin (a cholesterol–lowering drug) for 40 months avoids one death from coronary artery disease. No reduction in the rate of Caesarean section was observed.
So where does this leave us?
It remains to be verified in other studies and different settings that treating pregnant women with degrees of glucose intolerance (peak between normal and 7.8 mmol/l) improves their babies' growth and development and reduces adverse events in baby and mother. Nevertheless, it is apparent that without screening for gestational diabetes we would not now be in a position to ask these questions. Most women with more marked degrees of glucose intolerance and GDM would be missed without screening before 32 weeks of pregnancy.
The HAPO study cooperative Group 2008 Hyperglycemia and adverse pregnancy outcomes NEJM 258:1999-2002.
Ecker JL, Greene MF2008 Gestational diabetes-setting limits, exploring treatments NEJM 358:2061-2063.
Crowther CA et al 2005Effect of treatment of gestational diabetes mellitus on pregnancy outcomes NEJM 352:2477-2486.
Sermer et al 1995 Impact of increasing carbohydrate intolerance on maternal-fetal outcomes in 3637 women without gestational diabetes: the Toronto Tri-Hospital Gestational diabetes project Am J Obstet. Gynecol173:146-156
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