Gestational diabetes

RCT puts spotlight on overdiagnosis of gestational diabetes

The one-step oral glucose tolerance test (OGTT) screen for gestational diabetes almost doubles the number of women diagnosed compared to the two-step process but without any increase in maternal or perinatal complications.

The evidence, from a randomised controlled trial (RCT) of the two methods, supports simmering controversy and suggestions of overdiagnosis when using the IADPSG one-step approach preferred by the American Diabetes Association. The one-step approach is a two-hour fasting OGTT after a 75g glucose load.

The two-step Carpenter–Coustan screening approach is currently recommended by the American College of Obstetricians and Gynaecologists. It involves a 1-hour non-fasting glucose challenge test to 50g glucose followed by a 3-hour fasting OGTT to a 100g glucose for women in the range 7.2-11.1 mmol/L.

The RCT, published in the NEJM, comprised almost 24,000 women from Florida and Hawaii randomly assigned to either the one-step or two-step screening approach.

It found gestational diabetes was diagnosed in 16.5% of women using the one-step screen and 8.5% in women using the two-step approach.

However there was no significant difference between the groups in any of the other primary outcomes including large for gestational age infants, a perinatal composite outcome, gestational hypertension or preeclampsia, or caesarean section rates.

The study did find a lower adherence to screening with the fasting one-step approach (66%) compared to the two step approach (92%), but the results were similar in analyses that accounted for the differences in adherence.

“Although we did not find increased harms associated with the diagnosis and treatment of gestational diabetes in many more women with the one-step approach, some retrospective observational cohort studies have shown higher incidences of primary cesarean delivery and neonatal hypoglycaemia with one-step screening after conversion from two-step protocols, with no substantive improvement in outcomes,” the study said.

“Other considerations relevant to one-step screening include the burden on individual women of receiving a diagnosis of gestational diabetes on the basis of these milder criteria and the burden on the system of treating many more women.”

An editorial in the NEJM said there was still no agreement on the best approach to diagnosis of gestational diabetes.

“The current trial provides robust evidence that single-step, as compared with two-step, gestational diabetes screening resulted in the detection of gestational diabetes in almost one in five pregnant women, with no apparent maternal or perinatal benefit overall.”

“On the basis of the current data, however, the perinatal benefits of the diagnosis of gestational diabetes with the use of the IADPSG single-step approach appear to be insufficient to justify the associated patient and health care costs of broadening the diagnosis,” it said.

“Refocusing attention on interventions in women who are at risk for the development of diabetes is more likely to yield substantive benefits.”

Missed opportunities after gestational diabetes

Meanwhile an Australian led study has found women with a history of gestational diabetes do not understand their level of risk for developing type 2 diabetes.

An online survey of 429 women with previous gestational diabetes found 75% of women were overweight or obese. However this knowledge did not translate into a high level of perceived risk for developing type 2 diabetes.

Only a third of women (34%) thought they were at high risk of type 2 diabetes.

The researchers from the University of South Australia said 22% of women had not been tested for diabetes since having gestational diabetes.

“The priority is to educate both women with gestational diabetes, and the health professionals who care for them, to ensure greater communication and boost awareness of the risk factors these women have,” senior investigator Associate Professor Jennifer Keogh said.

“We also know that the most effective time to initiate and commit to healthy lifestyle and behaviour changes is up to two years post pregnancy, so interventions are likely to be more effective during this time frame.”

Most women reported family responsibilities and coping with hunger were the two main barriers to losing weight. Exercising was the most common strategy used for weight loss.

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