Should gestational diabetes be diagnosed at a lower threshold?

Commonly used thresholds for diagnosing gestational diabetes mellitus (GDM) may be too low. Indeed, treatment should be considered for pregnant women who are found to have mild hyperglycemia (MH), according to Montreal researchers. A study in the Canadian Journal of Diabetes found women treated for MH were significantly less likely to have fetal overgrowth compared to those who remained untreated for MH, and those who were treated for GDM. Notably, there is no consensus for the optimal glucose thresholds to diagnose GDM, the authors said. Yet GDM is a common complication that affects between 7% to 16% of pregnancies in Canada and is associated with an increased lifetime risk of type 2 diabetes (T2D) in both mothers and overweight babies.Uncontrolled glycemia is often accompanied with issues such as fetal overgrowth, preterm birth, gestational hypertension, and potential stillbirth or neonatal death. And fetal overgrowth, which leads to large-for-gestational-age (LGA) can lead to additional pregnancy complications, the study said. As such, it’s important to identify pregnancies that are at risk and monitor blood glucose.However, different guidelines differ in terms of their criteria for GDM diagnosis. For example, two important ones used by doctors in Canada—the Diabetes Canada (DC) 2018 guidelines and the International Association of Diabetes and Pregnancy Study Groups (IADPSG) recommendations—offer different criteria. The IADPSG suggests lower glucose values be used than the DC ones.The researchers compared whether treatment of GDM diagnosed based on lower glucose values, such as the IADPSG thresholds, had different pregnancy outcomes than in women diagnosed at high thresholds.To do the study, the researchers compared pregnancy outcomes at two different university affiliated hospitals in Montreal which happened to differ in practice. Both hospitals used a two-step approach to testing, but one used the IADPSG thresholds while the other used the thresholds defined by the DC guideline. “We defined second-step glucose values above the IADPSG thresholds but below the DC thresholds as ‘mild hyperglycemia’ (MH),” the paper said. MH was defined as intermediate glucose values that were diagnostic of GDM at one centre but not the other. This was fasting plasma glucose 5.1 to 5.2 mmol/L, 1-hour PG 10 to 10.5 mmol/L, or 2-hour PG 8.5 to 8.9 mmol/L.They assessed GDM-associated complication rates in people with treated MH and compared that to rates in women who were not treated for MH. Those numbers were then compared to complication rates in people who were diagnosed with GDM by DC thresholds at either centre. The retrospective study was conducted via a chart review of eligible cases at Centre A and Centre B. Patients who were included in the study all underwent GDM screening tests from September 2013 through February 2020. They all had GCT results between 24 and 28 weeks, and six days of gestation, that were between 7.8 and 11.0 mmol/L. Additional details relating to pregnancy and maternal healthy were taken into account. At both centres, the women underwent a fasting 2-hour 75-g OGTT. Centre A used the thresholds recommended by the DC, while Centre B used the lower IADPSG thresholds for diagnosing GDM. This meant there was a subgroup of women who were treated for GDM at Centre B but not at Centre A, the paper said. This was considered the MH group.A total of 840 women met the inclusion criteria and were included in the analyses. At Centre A, 247 patients had GDM as defined by the DC criteria, leaving 73 with untreated MH. Centre B had 483 women with CDM defined by DC threshold, and 82 with MH that was treated.The breakdown showed that at Centre A, where MH was not treated, the women with MH had a three-fold higher odds of LGA than women with DC threshold GDM: 21.9% compared to 8.5% respectively.At Centre B where MH was treated, women with MH had about a two-fold higher odds of LGA compared to women with DC-threshold GDM: 12.3% compared to 6.4%.“We observed that MH was consistently associated with fetal overgrowth compared with the diagnosis and treatment of GDM using higher glucose thresholds. Our findings signal that women with MH experience important increases in LGA and associated adverse events,” the study said.5Also, the odds of macrosomia were over 2-fold higher when comparing treated MH with GDM. As for what the Canadian guidelines say, the Canadian Healthcare Network was told by a spokesperson for Diabetes Canada “our pregnancy guidelines are currently in the process of being updated and will be published in the Canadian Journal of Diabetes this fall.

Should gestational diabetes be diagnosed at a lower threshold?

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