While it’s important for women to assess their endocrine function and maintain healthy blood glucose levels during pregnancy, is the glucose tolerance test the best way to do that?
Gestational diabetes mellitus (GDM) is an increasing problem among pregnant mothers in the U.S., affecting an average of approximately 7% of all pregnancies – over 200,000 cases annually. GDM significantly increases the risk of preeclampsia, premature and cesarean delivery, shoulder dystocia and other birth injuries, newborn hyperinsulinemia, transfer to neonatal intensive care, and newborn jaundice.
The current U.S. standard of care dictates that all pregnant women should be screened for GDM during weeks 24-28 of gestation via the glucose challenge test (GCT), in which a 50-gram glucose solution is administered and blood glucose is measured after 1 hour. Patients with a GCT result of >=130 mg/dL are then referred for the “gold standard” oral glucose tolerance test (OGTT), in which fasting blood glucose is measured and again at 1, 2, and 3 hours after a 75-gram or 100-gram solution is consumed. Patients with abnormal results in 2 or more of the 4 readings are then officially diagnosed with GDM. But how accurate are these tests? This meta-analysis of 26 studies found that the initial GCT screening identified only 76% of GDM cases, with a significant false positive rate of 15-23% of all women tested. Why is this significant?
Risks associated with Glucola drinks
Much has been written about the troubling ingredients in the Glucola drinks administered for the GCT. Potential fetal harm has been associated with genetically modified corn, bromated vegetable oil, and artificial food dyes. The sheer volume of pure simple sugar, taken on an empty stomach with no fats or protein to slow absorption, is enough to cause the nausea, vomiting, bloating, and headache many women experience.
To put this in perspective, 50-100 grams of carbs consists of about 30-60% of the entire standard recommended daily allowance of 175 grams of carbs for pregnant women, consumed in one sitting as simple sugar. The total sugar content of the 75-gram drink is approximately equivalent to that of 3 Snickers bars, about 3-1/2 cups of orange juice, or 5 medium bananas. Of course, this makes many people sick! Ironically, the population the test is designed to identify is at the highest risk of being harmed by the test itself. A “normal” 1-hour postprandial blood glucose result for the OGTT is defined as <= 180 mg/dL, and the accepted 2-hour postprandial result is <= 155 mg/dL. But studies suggest that nerve damage occurs at blood glucose levels starting at 140 mg/dL, while healthy, insulin-sensitive people rarely have blood glucose levels above 100 mg/DL two hours after eating. In short, drinking a solution of 50-100 grams of pure sugar – an unnatural quantity in any context – may be damaging even to healthy people.
Pregnant women are not asked to smoke entire packs of cigarettes to “challenge” their lung capacity, or drink shots of hard alcohol to test the robustness of their liver function. Measuring the endocrine function of potentially insulin-resistant pregnant women by administering a huge dose of genetically modified corn syrup, along with hydrogenated oil and artificial dye, may be counterproductive for both mother and baby.
Risks associated with GDM diagnosis
As noted above, receiving a diagnosis of GDM greatly increases a pregnant mother’s risk of interventions during pregnancy and childbirth. Women with this diagnosis are frequently denied care from midwives in free-standing birth centers, and therefore run a greater risk for epidural anesthesia, induced labor, and delivery via c-section. Babies born to diabetic mothers are more likely to be tested for hypoglycemia, transferred to the NICU, and bottle-fed formula, despite evidence demonstrating that skin-to-skin contact and breastfeeding (or receiving colostrum via syringe) actually produces better outcomes for these babies. Women with GDM are already at greater risk of experiencing low milk supply, so this cascade of interventions further increases the likelihood of breastfeeding difficulty or failure.
The purpose of universal glucose screening is to identify at-risk patients who can benefit from detection and management of hyperglycemia. Unfortunately, women diagnosed with GDM via the OGTT are likely to be counseled according to disadvantageous and outmoded ADA guidelines, suggesting “a variety of fresh fruits” and “limiting fat intake to 30% or less of daily calories.” Copious research suggests that lower-carb, higher-fat diets are more effective in managing diabetes.
Alternatives to the OGTT
Home Glucose Monitoring
Every pregnant mother can benefit from testing her blood glucose levels at home, although she may not benefit from having them written into her medical record. Home glucose monitors are relatively inexpensive, accurate, and often covered by insurance. Pregnant women can easily measure their first-morning fasting blood glucose level as well as their levels one or two hours after meals, over a period of several days or weeks, and evaluate which foods and other factors affect their blood glucose.
Many women with high readings can successfully bring their blood glucose within normal range by reducing their carbohydrate intake and/or safely increasing moderate exercise, circumventing the risks associated with an official diagnosis of GDM through their healthcare providers. Women unable to normalize their glucose levels through lifestyle changes may have more complicated health issues – this group would be particularly wise to forego consuming 50-100 grams of pure glucose solution. These women could share their home test results with healthcare providers and confirm a diagnosis with an A1C test, whereupon they can work with their providers to choose an appropriate treatment protocol.
A1C Blood Test
The A1C or HbA1C blood test, taken via simple blood draw, measures serum levels of glycated hemoglobin (hemoglobin exposed to plasma glucose), and thus reflects the patient’s average blood glucose level over several months. Because the A1C test reflects an average, normal results may obfuscate abnormal highs and lows. However, its overall accuracy surpasses the GCT for the purpose of screening pregnant women – one study found the A1C test to be 86% effective in identifying GDM, with only a 3% false positive rate.
Alternative sources of glucose for testing
Adverse reactions and patients’ increasing reluctance to take the GCT has engendered several alternatives to Glucola drinks, including administering the test after various combinations of fruit and juice are eaten or administering the jelly bean test. Many practitioners reject these methods as unreliable since the GCT results are based on pure glucose which is immediately absorbed into the bloodstream. The total sugar content of fruits and juices is partly comprised of fructose and sucrose, which are not immediately absorbed and yield inconsistent results. Jelly beans are sweetened with corn syrup (pure glucose) so they are a more accurate substitute, but the amount of glucose in jelly beans is not consistent and most brands also contain artificial dye and genetically modified corn syrup.
When a standard glucose test must be administered, organic corn syrup provides a reasonable Glucola alternative which yields equally precise results. The syrup can be measured by weight (mL=g) or volume to yield exactly 50, 75, or 100 grams of pure glucose without any harmful additives, and dissolved in water or other beverages.
While it’s important for women to assess their endocrine function and maintain healthy blood glucose levels during pregnancy, the GCT and OGTT may be harmful and unpleasant and don’t always lead to improved outcomes. Every pregnant woman has the right to decline glucose screening, and healthcare providers should support patients who prefer to monitor and manage their own blood glucose levels. When patient home management is impractical, lower-impact alternatives to Glucola drinks should be offered.
What are your thoughts about the glucose tolerance test during pregnancy?
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