Gestational diabetes is a condition where high blood sugar levels develop during pregnancy in individuals who did not have diabetes beforehand. This typically occurs between 24 and 28 weeks, when placental hormones can interfere with the body’s ability to use insulin effectively. Identifying and managing gestational diabetes is important because elevated blood sugar can lead to complications for both the pregnant individual and the baby.
Understanding Gestational Diabetes Before Testing
Before specific tests, medical professionals observed a connection between pregnancy and glucose intolerance. Early in the 20th century, understanding of diabetes in pregnancy relied on a patient’s medical history and observable symptoms. Dr. Priscilla White, in 1949, developed a classification system for diabetes in pregnancy. Uncontrolled high blood sugar during pregnancy could lead to increased risks for both the mother and the developing fetus, such as larger babies complicating delivery. These insights highlighted the need for better detection and management.
The First Attempts at Screening
Efforts to screen for gestational diabetes began in the mid-20th century. Initially, screening relied on assessing a patient’s medical history, but researchers recognized limitations for widespread detection. Dr. John O’Sullivan and statistician Claire Mahan made significant contributions in the 1950s and 1960s.
In 1957, O’Sullivan, Wilkerson, and Remein proposed a 3-hour oral glucose tolerance test (OGTT) for individuals with risk factors like a family history of diabetes or large babies. For those without known risk factors, they suggested a 1-hour blood glucose measurement after 50 grams of glucose, with a cutoff of 130 mg/dL considered abnormal, prompting a full 3-hour OGTT. Their 1964 work led to the two-step oral glucose tolerance test, providing the first statistically based criteria for assessing glucose levels in pregnancy. These methods allowed for systematic identification of glucose intolerance.
Establishing Diagnostic Standards
Following initial screening efforts, the medical community established more formal diagnostic criteria. The O’Sullivan and Mahan criteria, published in 1964, became the standard for detecting diabetes in pregnancy for decades, based on a 100-gram, 3-hour oral glucose tolerance test. In 1979, the First International Workshop on Gestational Diabetes Mellitus, organized by Norbert Freinkel, standardized the understanding of the condition. The workshop defined gestational diabetes as “carbohydrate intolerance of variable severity recognized for the first time in pregnancy” and recommended universal screening for all pregnant women between 24 and 28 weeks of gestation.
In the U.S., the National Diabetes Data Group (NDDG) adopted O’Sullivan’s 100-gram, 3-hour OGTT values, widely followed by organizations like the American Diabetes Association. While the World Health Organization (WHO) recommended a 75-gram, 2-hour OGTT, the NDDG’s 100-gram test remained prevalent in the U.S. The Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study (early 2000s) demonstrated a continuous relationship between glucose levels and adverse pregnancy outcomes. This led the International Association of Diabetes and Pregnancy Study Groups (IADPSG) to propose new diagnostic criteria in 2010, endorsed by WHO in 2013, focusing on a 75-gram, 2-hour OGTT and perinatal outcomes.
Current Screening Practices
Today, screening for gestational diabetes occurs between 24 and 28 weeks of pregnancy, though it may happen earlier for individuals with higher risk factors. Two primary approaches are used. The two-step approach, recommended by organizations like ACOG, involves an initial 50-gram, 1-hour glucose challenge test (no fasting required). If elevated, a diagnostic 100-gram, 3-hour OGTT confirms the diagnosis.
Alternatively, a one-step approach uses a single 75-gram, 2-hour OGTT, requiring fasting. Both methods identify gestational diabetes for timely management to support a healthy pregnancy for both the mother and the baby.