Glossary

Term · Pregnancy: Eating

Carpenter-Coustan criteria

Also: Carpenter-Coustan, Carpenter and Coustan thresholds

The set of blood sugar cut-offs used to read the three-hour glucose test for gestational diabetes. Other labs and guidelines use different numbers.

In plain words

The Carpenter-Coustan criteria are a set of blood sugar numbers used to decide whether a person has after a glucose test. The test usually involves drinking a sweet drink and having blood drawn at set times over three hours. The criteria set a cut-off for each draw. If two or more of the readings are at or above their cut-offs, the result counts as positive. These numbers were widely used in the United States for many years. Other guidelines use different cut-offs, so a result can read differently depending on which set a clinic uses. Mothers can ask which set was used. The numbers describe a lab threshold, not a verdict on the pregnancy.

The deeper version

The Carpenter and Coustan criteria (Carpenter and Coustan, American Journal of Obstetrics and Gynecology, 1982) define a positive 100-gram, three-hour as two or more of four plasma values meeting or exceeding 95 (fasting), 180 (one hour), 155 (two hours), and 140 (three hours) milligrams per deciliter. Newer sets, including the 2010 International Association of Diabetes and Pregnancy Study Groups thresholds based on a 75-gram test, differ, and ACOG's Practice Bulletin No. 190 (2018) describes both one-step and two-step strategies. The HAPO study (Metzger and colleagues, New England Journal of Medicine, 2008) showed continuous associations between maternal glucose and perinatal outcomes, which fueled debate about where to set cut-offs and how many pregnancies to label as diabetic.

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Sources

  • Carpenter MW, Coustan DR — Criteria for screening tests for gestational diabetes. American Journal of Obstetrics and Gynecology, 1982
  • American College of Obstetricians and Gynecologists — Practice Bulletin No. 190: Gestational Diabetes Mellitus, 2018

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