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Panel Calls for Lower Gestational Diabetes Cutoffs

Lower glucose thresholds for gestational diabetes called for by an international consensus panel may double and possibly even triple the number of women diagnosed. 

Two to three times more pregnant women may soon be diagnosed and treated for gestational diabetes, based on proposed measurements for determining blood glucose levels for the mother and unborn baby, according to a new study. 

The new criteria require only a single measurement of fasting plasma glucose of 92 mg/dl or higher or a glucose tolerance test level of at least 180 mg/dl at one hour or 153 mg/dl at two hours.

In high-prevalence countries like the U.S., all pregnant women should undergo diagnostic 75-g oral glucose tolerance testing, the consensus panel recommended in the March issue of Diabetes Care.

The recommendations are a sharp departure from guidelines in many countries.

Although uniform international standards have been lacking, these levels had generally been considered safe and in the normal range during pregnancy. The American Diabetes Association recommends risk-based screening only with a typically two-step process for diagnosis: first a nonfasting glucose challenge, then a formal glucose tolerance test for confirmation.

ADA diagnostic thresholds are 95 mg/dl for fasting glucose, 180 mg/dl for a 100-mg glucose tolerance test at one hour, and 155 mg/dl at two hours. Although the difference from the new recommendations is small, the number of women identified with gestational diabetes will be substantially greater, said Boyd E. Metzger, MD, of Northwestern University in Chicago, who led the consensus group.

Under current U.S. guidelines, just 5% to 8% of women receive a gestational diabetes diagnosis, he noted in an interview.

In the large international Hyperglycemia and Adverse Pregnancy Outcome (HAPO) trial — also led by Metzger — that formed the primary basis for the group’s deliberations, up to 16.1% of pregnant women met at least one of the criteria.

The new thresholds were set to reflect risk of perinatal harm rather than the mother’s future risk of diabetes or derivation from nonpregnant populations as has been the case in the past.

The HAPO trial had shown no glucose cutoff for these risks, so the panel set their diagnostic criteria at the level at which there was a 75% increased risk compared with the median for:

  • Birth weight above the 90th percentile
  • Cord C-peptide above the 90th percentile, a marker of the baby’s insulin levels
  • Infant percent body fat above the 90th percentile

Metzger stated that, “At these thresholds, the risk was doubled for a large-for-gestational-age baby, preeclampsia, and toxemia of pregnancy and rose significantly for cesarean delivery as well.”

The good news is that trials have shown treating mild gestational diabetes — the majority of cases likely added by the lower glucose criteria — effectively reduced many of these risks with few women needing anything more than lifestyle changes, he noted.

However, the proposed guidelines would have to be adopted by organizations like the American Congress of Obstetricians and Gynecologists to benefit women and children.

The American Diabetes Association has already started evaluating the recommendations, although whether it will adopt them remains to be seen, Metzger said.

One hurdle for adoption may be the increase in costs associated with the additional diagnoses, cautioned Robert G. Moses, MD, of the South Eastern Sydney and Illawarra Area Health Service in Wollongong, Australia.

In his editorial in the same issue of Diabetes Care, Moses noted that physicians may actually find the new guidelines more convenient and thus improve adherence by eliminating the need to get women to return for a second glucose tolerance test.

Practice Pearl: Note that the American Diabetes Association recommends risk-based screening only with a typically two-step process for diagnosis that differs from the proposed guidelines from the consensus panel.

Metzger BE, et al “International association of diabetes and pregnancy study groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy” Diabetes Care 2010; 33: 676-82.