Informed Choice and Informed Refusal for Gestational Diabetes Screening
Direct Answer
Women who cannot tolerate the standard 75-gram oral glucose tolerance test retain the right to informed refusal of gestational diabetes screening, but they must be counseled that declining screening carries documented risks of undetected hyperglycemia leading to macrosomia, shoulder dystocia, preeclampsia, neonatal hypoglycemia, and long-term maternal type 2 diabetes—and that alternative screening methods exist that may be more tolerable. 1, 2
Understanding the Clinical Context
Universal screening at 24–28 weeks gestation is the standard of care because the HAPO study demonstrated a continuous relationship between maternal glucose levels and adverse outcomes (macrosomia, cesarean delivery, neonatal hypoglycemia, shoulder dystocia) with no clear threshold for risk. 1, 2
The U.S. Preventive Services Task Force assigns a B-grade recommendation (moderate net benefit) to universal screening at 24–28 weeks, citing reductions in preeclampsia, fetal macrosomia, and shoulder dystocia. 2
Treatment of gestational diabetes reduces serious perinatal complications, with a number needed to treat of 34 to prevent outcomes such as macrosomia and shoulder dystocia. 2
Alternative Screening Options When Standard OGTT Is Not Tolerated
Two-Step Approach (More Tolerable Initial Screen)
The American College of Obstetricians and Gynecologists endorses a two-step strategy that begins with a 50-gram glucose challenge test (non-fasting) at 24–28 weeks, which is generally better tolerated than the 75-gram test. 1, 2, 3
If the 1-hour plasma glucose is ≥130–140 mg/dL, the patient proceeds to a diagnostic 100-gram OGTT (fasting), which requires at least two abnormal values for diagnosis: fasting ≥95 mg/dL, 1-hour ≥180 mg/dL, 2-hour ≥155 mg/dL, 3-hour ≥140 mg/dL. 1, 2, 3
The 50-gram screen does not require fasting and is more patient-friendly, making it a reasonable first-line alternative for women who struggle with the 75-gram test. 3, 4
Fasting Glucose Alone (Limited but Feasible)
A fasting plasma glucose ≥92 mg/dL at 24–28 weeks meets the diagnostic threshold for gestational diabetes using the one-step IADPSG criteria, even without completing the full OGTT. 1, 2
This approach will miss cases where only the 1-hour or 2-hour values are elevated, but it provides some screening when the full test is not feasible. 2
Home-Based Capillary Testing (Emerging Option)
The GTT@home device has been evaluated for home-based OGTT using capillary blood samples, showing 79.8% of results in the lowest-risk category compared to laboratory venous samples, with agreement in classification in 54/61 cases. [@10@]
This device may offer a future alternative for women unable to attend clinic-based testing, though it is not yet widely adopted in standard practice. 5
Counseling for Informed Refusal
Risks of Declining Screening
Untreated gestational diabetes is associated with higher incidence of macrosomia, shoulder dystocia, preeclampsia, neonatal hypoglycemia, and cesarean delivery. [@3@, @7@]
Women with undiagnosed gestational diabetes have a 3.4-fold increased risk of developing type 2 diabetes postpartum, and early detection allows for preventive interventions. [@3@, @5@]
The HAPO study demonstrated that even mild hyperglycemia carries continuous risk, meaning that declining screening may leave clinically significant glucose intolerance undetected. [@1@, 2]
Documentation of Informed Refusal
Document the patient's understanding of the risks of undetected gestational diabetes, including fetal macrosomia, birth trauma, and long-term maternal metabolic disease. [@3@, @7@]
Document that alternative screening methods were offered (two-step approach, fasting glucose alone) and the reasons for refusal. [@3@, @4@]
Offer repeat counseling at subsequent visits, as patient tolerance and preferences may change as pregnancy progresses. 2
Special Considerations
High-Risk Women Require More Intensive Counseling
Women with BMI ≥30 kg/m², prior gestational diabetes, first-degree relative with diabetes, or high-risk ethnicity (Hispanic, Native American, South/East Asian, African American, Pacific Islander) should receive early screening at the first prenatal visit and repeat screening at 24–28 weeks if initial results are negative. 1, 2
Declining screening in high-risk women carries substantially greater risk, as these populations have higher baseline prevalence of gestational diabetes (15–20% with one-step criteria vs. 5–6% with two-step). [2, @4@]
Glycosuria Is Not a Reliable Screening Tool
Glycosuria in pregnancy does not reliably indicate hyperglycemia because the renal threshold for glucose decreases during pregnancy due to increased glomerular filtration rate and reduced tubular reabsorption. [@5@]
Urine glucose testing is not recommended for routine care or treatment decisions and should not be used as a substitute for blood glucose screening. 6
Postpartum Follow-Up Remains Essential
Even if screening is declined during pregnancy, all women at high risk should undergo a 75-gram OGTT at 4–12 weeks postpartum using non-pregnancy diagnostic criteria to detect persistent diabetes or prediabetes. [1,2, @5@]
Lifelong diabetes screening every 3 years is recommended for women with risk factors, regardless of whether gestational diabetes was diagnosed during pregnancy. [@1@, 2]
Common Pitfalls to Avoid
Do not accept "I can't tolerate the test" without exploring alternative methods (two-step approach, fasting glucose alone, or home-based testing). [@3@, 3, @10@]
Do not use hemoglobin A1c as a substitute for OGTT screening, as it has poor sensitivity and specificity for detecting gestational diabetes. [@3@]
Do not rely on random glucose measurements or glycosuria as screening tools, as they are not validated for gestational diabetes diagnosis. [@3@, 6]
Do not skip repeat screening at 24–28 weeks in high-risk women who had negative early screening, as insulin resistance increases exponentially in the second and third trimesters. [@3