glucose tolerance screening.

Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with onset or first recognition during pregnancy.¹

The Second International Workshop Conference on Gestational Diabetes recommends that all pregnant women be routinely screened for gestational diabetes between the 24th and 28th week of pregnancy.²

If a woman is diagnosed with gestational diabetes, she may be considered at risk for complications such as having a large baby, fetal death in utero, or stillbirth. However, perinatal mortality rates are difficult to attribute solely to gestational diabetes.

Large babies and complications associated with delivering them—such as shoulder dystocia or cesarean delivery—may sometimes be related to maternal obesity rather than a diabetic condition alone.

Common Screening Tests

Two primary tests are commonly used to measure maternal glucose levels and identify possible gestational diabetes.

The Glucose Challenge Test

Most pregnant women are offered the glucose challenge test.

This screening involves drinking a beverage containing 50 grams of glucose—commonly called glucola. One hour later, a blood sample is taken to measure plasma glucose levels.³

The Glucose Tolerance Test

Women considered to be at higher risk for developing diabetes—due to factors such as age, obesity, family history, or a history of delivering a large baby or experiencing stillbirth—may be encouraged to take the glucose tolerance test.

For this test, the woman consumes a beverage containing 100 grams of glucose, and her blood sugar levels are measured over a three-hour period.⁴

If a woman receives a positive or borderline result on the initial 50-gram, one-hour screening test, she is usually advised to undergo the more extensive 100-gram, three-hour test.

An Alternative to the Glucose Drink

For women who dislike the glucola drink, a surprising alternative has been studied: jelly beans.

Research has shown that eating 28 jelly beans—equivalent to approximately 50 grams of simple carbohydrates—can be used as a sugar source for gestational diabetes screening.⁵

Studies found that both the glucose beverage and jelly beans produced similar screening results. However, women reported fewer adverse side effects with jelly beans and were less likely to experience nausea or illness.

The Impact of a Diagnosis

A survey of obstetricians revealed that 94 percent perform the glucose challenge test on all of their pregnant patients.⁶

Once a woman receives the diagnosis of gestational diabetes—even if the condition is well controlled during pregnancy—she is often classified as “high risk.” This classification may increase the likelihood of interventions, including cesarean delivery, because physicians anticipate a larger baby and potential birth complications.⁷

Concerns About Test Accuracy

Glucose testing during pregnancy remains controversial, in part because results can be difficult to reproduce consistently.

Women are often tested without consideration of the time since their last meal or the time of day the test is performed. Blood sugar levels can vary from day to day, and the reasons for these fluctuations are not always clear.⁸

In some cases, the test may fail to identify gestational diabetes altogether. When pregnant women were tested on two consecutive days using the 50-gram, one-hour glucose challenge test, approximately ten percent of women who had gestational diabetes received test results that did not indicate the condition.

In another study involving 21 women, researchers found no meaningful difference in screening results between women with diabetes and those without it.⁹

Screening in Subsequent Pregnancies

If a woman was screened for gestational diabetes during a previous pregnancy and received normal results, it may not always be necessary to repeat the screening in later pregnancies.

Women with normal glucose readings in a prior pregnancy have less than a one percent chance of developing gestational diabetes within four years.¹⁰

If a woman chooses not to undergo further screening, it is important that she discuss this decision with her physician.

Debate Within the Medical Community

A review published in 1989 examining gestational diabetes and screening methods reported that the glucose tolerance test was poorly reproducible. The authors also stated that the perinatal illness and death associated with gestational diabetes had been “considerably overemphasized” and that no population had yet been clearly shown to benefit from screening, diagnosis, and treatment.¹¹

Their conclusion was striking:

“Except for research purposes, all forms of glucose tolerance testing should be stopped.”

The American Diabetes Association has taken a more moderate position. The organization recommends that women who are under 25 years old, of normal weight, and have no family history or other risk factors may not need to be screened for gestational diabetes.¹²

This recommendation differs from the policies of the American College of Obstetricians and Gynecologists (ACOG), whose members typically support universal screening for all pregnant women regardless of individual risk factors.¹³

Making an Informed Decision

Differences in opinion among medical organizations are not uncommon. Obstetric practice has historically favored proactive testing rather than a “wait-and-see” approach.

However, much of what the medical establishment does in the name of protecting patient health is not always supported by strong clinical evidence.

If you believe glucose screening is important for your pregnancy, you may choose to undergo the test. But it is equally important not to accept routine procedures without understanding their limitations, inconsistencies, and possible consequences.

In the case of gestational diabetes screening, those consequences may include misdiagnosis and an increased likelihood of cesarean delivery.

— Kim French