A large study of about 27,000 pregnant women, termed the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) trial, evaluated risks of high blood sugar (hyperglycemia) that developed during pregnancy. The HAPO study found that risk to babies increases gradually as glucose levels increase, even at values that are lower than those currently used to diagnose gestational diabetes. Based largely on the results of the HAPO study, IADPSG developed new guidelines for screening and diagnosis of gestational diabetes and published their recommendations in the March issue of Diabetes Care.
The current guidelines of the American Diabetes Association (ADA) recommend screening women in the second trimester of pregnancy (after about 20-24 weeks of pregnancy) by measuring their blood sugar after giving a small amount of glucose; if the levels are too high, a full glucose tolerance test, using a larger amount of glucose is given. Diabetes is diagnosed if two or more of the values in the glucose tolerance test are abnormal.
The IADPSG guidelines suggest a different approach than the current ADA guidelines. The IADPSG guidelines recommend screening all women at their first doctor's visit early in pregnancy, using the current criteria to diagnose diabetes in the general population. The goal here is to identify diabetes that is already present but not diagnosed. These women are already diabetic, and care should be started to control their blood sugar. The guidelines then suggest doing a full glucose tolerance test in the second trimester of pregnancy, without doing the screen with the small amount of glucose first.
The other major change in the IADPSG guidelines is that only one of the values has to be abnormal to diagnose diabetes, instead of two using the ADA criteria. Some of the cut-off values are slightly lower in the IADPSG guidelines as well. The lower cut-offs were selected as the values at which the risk of a baby having diabetes-related complications during pregnancy increased by 75%.
Impact of Recommendations
The expected benefit of the new guidelines is that it might reduce the number of babies who have problems related to high blood sugar in their mothers. These problems include premature birth and death, low blood sugar (hypoglycemia) after birth, and being larger, fatter babies. Several studies have shown that women diagnosed using the ADA criteria and treated for diabetes have babies with fewer of these complications. The HAPO trial showed that risk of having babies with these complications rises at glucose values even lower than those used currently, but did not provide any evidence that treating these can reduce complications. Estimates from the HAPO study are that about twice as many women would be diagnosed as having gestational diabetes based on the IADPSG criteria than are diagnosed using the ADA criteria.
Physicians and women might welcome the new guidelines because they offer convenience by eliminating the need for women to return to doctors' offices for a second glucose test, says an accompanying editorial by Robert G. Moses, MD, of the South Eastern Sydney and Illawarra Area Health Service. But the costs associated with the additional diagnoses might present a hurdle to widespread adoption of the guidelines. Under the criteria in the new guidelines, the proportion of pregnant women with gestational diabetes would be an estimated 18%, about double the current figures. "Clearly the implications of this doubling will need serious consideration," Moses writes.
These proposed new guidelines have already provoked a number of professional organizations to consider whether or not to change their criteria for diagnosing diabetes. Until these decisions are made, it is unlikely that the proposed new guidelines will actually be used by most physicians caring for pregnant women.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Moses, Robert G. New Consensus Criteria for GDM: Problem Solved or a Pandora's Box? Diabetes Care. March 3, 2010. Pages 690-691.
Phend, Crystal. Panel Calls for Lower Gestational Diabetes Cutoff. MedPage Today. Available online at http://www.medpagetoday.com/OBGYN/Pregnancy/18716 through http://www.medpagetoday.com. Published February 27, 2010. Accessed March 18, 2010.