Impaired glucose tolerance, low HDL cholesterol and age > 35 were the strongest predictors of developing diabetes in women with gestational diabetes mellitus (GDM), a study from Vienna has found.

GDM is defined as any degree of glucose intolerance with first onset or recognition during pregnancy. Recurrence rates in subsequent pregnancies are high and it is thought that women who develop GDM are at enhanced risk of developing diabetes.

In a prospective observational study, 110 women with GDM were followed up after the affected pregnancy with regular metabolic screening. Forty one pregnant women without GDM formed the comparator group.

Over a ten-year follow-up period 23 (21%) of the women with GDM went on to be identified with diabetes. Metabolic variables measured at baseline during the index pregnancy were compared with the later development of diabetes.

High risks of developing diabetes were associated significantly with: higher maternal age, higher fasting plasma glucose and 2-hour oral glucose tolerance tests, higher triglyceride levels and blood pressure, waist circumference > 88 cm, BMI > 30 kg/m2 and lower HDL-cholesterol. In short, the criteria used to identify the metabolic syndrome were all significant predictors of the risk of developing diabetes. Needing insulin therapy and insulin resistance during pregnancy were also significant risk factors.

The best independent predictors for developing diabetes were: impaired glucose tolerance, hazard ratio (HR) 6.77 (95% CI: 2.96-15.45, p< 0.001); HDL cholesterol < 50 mg/dl, HR 2.88 (95% CI: 1.24-6.67, p=0.010) and age > 35, HR 3.06 (95% CI: 1.32-7.12, p=0.006). Women with at least two risk factors had a higher risk of developing diabetes compared with those with only one, HR 3.2 (95% CI: 1.4-7.7, p=0.008)

Having two or three risk factors was associated with a significantly higher rate of progression compared with having just one: 54.5% in the former category progressed to overt diabetes compared with 20.8% in the latter.

The development of type 2 diabetes appears to be a continuously progressive process which can last for years or even decades. The metabolic stress of pregnancy appears to unmask this tendency temporarily, even though most women will become euglycaemic after delivery. The underlying metabolic disorder for many of these women will however continue to progress. GDM is an independent risk factor for diabetes. The opportunities for timely intervention and prevention here are obvious. Primary care is best placed to offer this help.

Dr Chris Barclay