Gestational diabetes (GDM) guidelines

Gestational DM (GDM) is a type of diabetes (carbohydrate intolerance) with onset or first recognition during pregnancy. It affects approximately 7% of all pregnancies.

Universal screening is recommended (ie. all pregnant women should be screened for it). It is screened/ tested for with an oral glucose tolerance test (OGTT).

Some risk factors for GDM include:
– Glycosuria (glucose in your urine);
– Age over 30 years;
– Obesity;
– Family history of diabetes;
– Past history of GDM or glucose intolerance;
– Previous adverse pregnancy outcome;
– Belonging to a particular ethnic group (higher risk groups in Australia include:  Indigenous Australians, Polynesians, South Asians, Middle Eastern, other Asians).

The screening test should be performed at 26-28 weeks’ gestation. Positive results are:
– 1 hour venous plasma glucose level 7.8 mmol/L after a 50 g glucose load (morning, non-fasting); or
– 1 hour venous plasma glucose level 8.0 mmol/L after a 75 g glucose load (morning, non-fasting).

Confirmation of diagnosis after a positive screening test:
– A 75 g OGTT (fasting) with a venous plasma glucose level at 0 hours of 5.5 mmol/L and/or at 2 hours of 8.0 mmol/L

Why should we care about GDM? Just the other day a friend told me ‘my mate had GDM but it’s no big deal because it just goes away’. Well, not exactly… It can result in both short and long-term complications for both baby and mother.

Foetal complications:
– Macrosomia (birth weight >4kg);
– Neonatal hypoglycaemia; (low blood sugars in the newborn)
– Perinatal morbidity (eg. shoulder dystocia); (disease in the newborn)
– Perinatal mortality; (death of the newborn)
– Congenital malformations (birth defects; increased 3-8x in infants of diabetic mothers);
– Hyperbilirubinaemia; (high levels of bilirubin in the blood)
– Polycythaemia; (too many red blood cells)
– Hypocalcaemia; (low levels of calcium)
– Respiratory distress syndrome; (pretty self-explanatory)
– Long-term complications: glucose intolerance, diabetes, obesity.

Maternal complications:
– Hypertension;
– Pre-eclampsia; (high blood pressure and protein in the urine of pregnant women)
– Increased risk of Caesarean section.

At present there are is no exact cut-off of maternal hyperglycaemia that causes an adverse outcome in the offspring.

Pregnancy should be continued to full term unless there is evidence of obstetric complications, eg: macrosomia, polyhydramnios, poor metabolic control, other obstetric complications (eg. pre-eclampsia, intrauterine growth retardation)

Management of GDM
– I won’t go into great detail but simply put it usually consists of lifestyle measures +/- medications;
– A recent Cochrane review has found that current studies are too small for reliable conclusions about which types of dietary advice are most suitable for women with GDM;
– One recent randomised controlled trial has found that treating women with GDM with a low-carbohydrate diet did not reduce the number of women needing insulin, and produced similar pregnancy outcomes;
– When looking at the benefits and harms of treating GDM, a large study for the U.S. Preventive Services Task Force found that treating GDM results in less pre-eclampsia, shoulder dystocia, and macrosomia; however, current evidence does not show an effect on neonatal hypoglycemia or future poor metabolic outcomes. The authors state that there is little evidence of short-term harm of treating GDM other than an increased demand for services.

Needless to say, the evidence is varying on recommended management; so if you are found to have GDM, please follow the advice of your doctor, and if you have any concerns, please discuss them with him/her.

Post-delivery follow-up:
– Maternal follow-up with OGTT at 6-8 weeks, then
– Every 1-2 years for women with normal OGTT (if potential for further pregnancies), OR
– Every 3 years (if pregnancy not possible)

Anyway, will keep you posted on my test results… fingers crossed!

Royal Australian & New Zealand College of Obstetrics & Gynaecologists
The Australasian Diabetes in Pregnancy Society
 Moreno-Castilla C, Hernandez M, Bergua M, et al. Low-Carbohydrate Diet for the Treatment of Gestational Diabetes: A randomized controlled trial. Diabetes Care. 2013 Apr 5.
 Han S, Crowther CA, Middleton P, et al. Different types of dietary advice for women with gestational diabetes mellitus. Cochrane Database Syst Rev. 2013 Mar 28;3.
 Hartling L, Dryden DM, Guthrie A, et al. Benefits and Harms of Treating Gestational Diabetes Mellitus: A Systematic Review and Meta-analysis for the U.S. Preventive Services Task Force and the National Institutes of Health Office of Medical Applications of Research. Ann Intern Med. 2013 May 28.

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