From the Guidelines
Approximately 7% of pregnant women fail the glucose tolerance test (GTT) and are diagnosed with gestational diabetes mellitus (GDM), according to the U.S. Preventive Services Task Force recommendation statement 1. The exact failure rate varies depending on the population being tested and the specific diagnostic criteria used. Most healthcare providers conduct this screening between 24-28 weeks of pregnancy, though women with risk factors may be tested earlier. The test typically involves drinking a glucose solution and having blood drawn one or more times to measure how effectively the body processes sugar. Women who fail the initial screening usually undergo a more comprehensive three-hour GTT for definitive diagnosis. The increasing prevalence of obesity, advanced maternal age, and family history of diabetes are contributing to higher rates of GTT failures in recent years. Some key points to consider include:
- The prevalence of GDM in the United States is 1% to 25%, depending on patient demographics and diagnostic thresholds 1.
- Pregnant women with gestational diabetes are at increased risk for maternal and fetal complications, including preeclampsia, fetal macrosomia, and neonatal hypoglycemia 1.
- Women with GDM are also at increased risk for type 2 diabetes mellitus; approximately 15% to 60% of women develop type 2 diabetes within 5 to 15 years of delivery 1.
- The U.S. Preventive Services Task Force recommends screening for GDM after 24 weeks of gestation, but screening may occur earlier in high-risk women 1.
- Treatment of screen-detected GDM with dietary modifications, glucose monitoring, and insulin (if needed) can significantly reduce the risk for preeclampsia, fetal macrosomia, and shoulder dystocia 1. The most recent and highest quality study, published in 2014, recommends that all pregnant women not known to have prior diabetes undergo a 75-g OGTT at 24–28 weeks of gestation 1. This study also notes that the anticipated increase in the incidence of GDM diagnosed by these criteria would have significant impact on the costs, medical infrastructure capacity, and potential for increased “medicalization” of pregnancies previously categorized as normal. However, the benefits of treatment on long-term metabolic outcomes in women who are treated for GDM compared with those who are not treated is uncertain 1.
From the Research
Percentage of Women Failing the Glucose Tolerance Test
- The exact percentage of women failing the glucose tolerance test (GTT) is not directly stated in the provided studies, but we can infer some information from the data:
- Approximately 1% of all pregnant women develop gestational diabetes, as stated in the study 2.
- A study from 1997 found that among 595 patients, 544 (91.4%) were screened with a 1-hour 50-g OGTT, and 76 women (12.8%) had a positive initial screening test 3.
- Another study from 2021 mentions that approximately 15% to 20% of screened women require the 100 g, 3-hour oral glucose tolerance test, depending on the cutoff used and population risk factors 4.
- It's essential to note that the percentage of women failing the GTT may vary depending on the population, risk factors, and the specific testing protocol used.
Risk Factors and Predictors of Gestational Diabetes
- Studies suggest that certain risk factors, such as family history, obesity, and previous history of gestational diabetes, can increase the likelihood of developing gestational diabetes 3, 5.
- Fasting glucose level during the oral glucose tolerance test has been identified as a predictor of the need for insulin in gestational diabetes 6, 5.
- A cut-off value of 105mg/dl for fasting glucose level on OGTT has been suggested to predict the need for insulin treatment in GDM 6.
- Other predictors of metformin failure in GDM include higher maternal age, fasting glucose level at OGTT, HbA1c at OGTT, and earlier gestational age at medication initiation 5.