Gestational diabetes mellitus (GDM) is one of the most common medical conditions encountered during pregnancy, affecting up to 9–14% of pregnancies worldwide depending on the population and diagnostic criteria used. Despite its prevalence, GDM often develops without noticeable symptoms, making universal screening essential. The standard glucose challenge test performed between 24 and 28 weeks of gestation has been the cornerstone of detection for decades. However, a growing body of evidence indicates that delaying GDM screening—either by missing the recommended window or by deferring diagnosis in high-risk women—carries substantial and preventable risks for both the mother and the developing fetus. This article examines the risks of delayed GDM screening, the pathophysiological underpinnings of the condition, and evidence-based recommendations to ensure timely detection and management.

Understanding Gestational Diabetes Mellitus

What Is GDM and How Does It Develop?

Gestational diabetes mellitus is characterized by glucose intolerance that is first recognized during pregnancy. During a normal pregnancy, the placenta produces hormones such as human placental lactogen, estrogen, progesterone, and cortisol. These hormones naturally induce a state of insulin resistance in maternal tissues, ensuring that an adequate supply of glucose is available for the growing fetus. In most women, the pancreas compensates by increasing insulin secretion. In GDM, however, the maternal pancreatic beta cells cannot produce enough insulin to overcome pregnancy-induced insulin resistance, resulting in hyperglycemia. This typically emerges in the second trimester, which is why the standard screening window of 24–28 weeks was selected—it captures most cases of GDM after the peak of placental hormone production.

Prevalence and Recognized Risk Factors

The incidence of GDM has risen significantly over the past two decades, paralleling increases in maternal obesity, advanced maternal age, and sedentary lifestyles. Women with body mass index (BMI) greater than 30 kg/m2 are at a two- to threefold higher risk of developing GDM. Additional risk factors include a family history of diabetes (especially in a first-degree relative), previous GDM, prior delivery of a macrosomic infant (≥4000 g), polycystic ovary syndrome (PCOS), a history of unexplained stillbirth, and belonging to certain ethnic groups with higher diabetes prevalence (e.g., Hispanic, African American, Native American, South or East Asian, and Pacific Islander). Women with multiple risk factors often develop GDM earlier in pregnancy and tend to have more severe hyperglycemia.

Why Early Screening Matters for High-Risk Women

The standard screening window at 24–28 weeks was chosen to optimize detection while avoiding unnecessary early testing. However, women with significant risk factors can develop GDM before 24 weeks, sometimes as early as the first trimester. Delaying screening in these populations means that the fetus may be exposed to sustained hyperglycemia during critical periods of organogenesis in the first trimester and rapid fetal growth in the early second trimester. Emerging evidence supports early GDM screening for high-risk women at the first prenatal visit or before 20 weeks, with repeat testing at 24–28 weeks if negative. The American College of Obstetricians and Gynecologists (ACOG) endorses this risk-based approach to identify and manage early-onset GDM.

Consequences of Delayed GDM Screening and Diagnosis

Maternal Complications

Delayed diagnosis of GDM increases the duration of uncontrolled hyperglycemia, directly raising the risk of several adverse maternal outcomes. Preeclampsia is one of the most serious: sustained high blood glucose contributes to endothelial dysfunction, systemic inflammation, and vasoconstriction. Women with untreated GDM have a two- to threefold higher risk of developing preeclampsia compared with normoglycemic controls. Preeclampsia can progress to eclampsia, HELLP syndrome, and maternal organ damage if not managed emergently.

Additionally, delayed screening means the baby may grow excessively large (macrosomia). For the mother, delivering a macrosomic infant significantly raises the likelihood of perineal lacerations, postpartum hemorrhage, and emergency cesarean section. Cesarean delivery carries surgical risks including infection, thromboembolism, and longer recovery. Undiagnosed GDM also increases the rate of operative vaginal delivery (forceps or vacuum), which can injure pelvic floor structures. Beyond the immediate pregnancy, women who experienced GDM and were not diagnosed or treated in a timely manner face a substantially higher risk of developing type 2 diabetes within 5–10 years postpartum. One large meta-analysis found that women with a history of GDM have a sevenfold increased risk of progressing to type 2 diabetes compared with women with normoglycemic pregnancies.

Fetal and Neonatal Complications

Fetal exposure to excess maternal glucose leads to fetal hyperinsulinemia, which in turn promotes excessive glucose uptake and fat deposition. This results in large-for-gestational-age (LGA) infants and macrosomia. Macrosomia is defined as birthweight ≥4000 grams (or ≥4500 grams depending on criteria) and occurs in 15–20% of pregnancies complicated by untreated GDM. Macrosomic infants are at high risk for shoulder dystocia during vaginal delivery, a potentially catastrophic event that can cause brachial plexus injury (Erb’s palsy), clavicle fracture, and severe perinatal asphyxia. Even with cesarean delivery, macrosomic infants have higher rates of respiratory distress syndrome and admission to the neonatal intensive care unit (NICU).

Neonatal hypoglycemia occurs in 25–50% of infants born to mothers with poorly controlled GDM. After birth, the infant’s pancreas continues to secrete excessive insulin, but the supply of maternal glucose is abruptly cut off. This can lead to symptomatic hypoglycemia, seizures, and long-term neurodevelopmental impairment if not promptly corrected. Other neonatal complications include polycythemia, hyperbilirubinemia (jaundice), and hypocalcemia. Delayed or absent GDM screening deprives healthcare teams of the opportunity to implement maternal glycemic control, fetal surveillance, and a coordinated plan for delivery and neonatal monitoring.

Long-Term Health Consequences for Offspring

The effects of in utero exposure to hyperglycemia extend well beyond the neonatal period. Offspring of mothers with untreated GDM are at increased risk of developing obesity, impaired glucose tolerance, and metabolic syndrome during childhood and adolescence. This is thought to occur through developmental programming—a concept known as the “Barker hypothesis” or “fetal origins of adult disease.” Animal and human studies have shown that intrauterine hyperinsulinemia alters the fetal hypothalamic-pituitary axis, appetite regulation, and pancreatic beta cell development. By adulthood, these individuals exhibit higher rates of type 2 diabetes, cardiovascular risk factors, and even nonalcoholic fatty liver disease. Delaying GDM screening thus perpetuates a cycle of intergenerational metabolic disease.

Evidence from Clinical Studies on Screening Timing

Robust data support the universal benefits of screening all pregnant women for GDM at 24–28 weeks. The landmark Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, a large multinational observational cohort, demonstrated a continuous linear relationship between maternal glucose levels on oral glucose tolerance tests and adverse pregnancy outcomes, even at levels below the diagnostic threshold for diabetes. Subsequent randomized trials—most notably the Australian Carbohydrate Intolerance Study in Pregnant Women (ACHOIS) and the Maternal-Fetal Medicine Units Network (MFMU) trial—showed that treating GDM diagnosed at 24–30 weeks significantly reduced rates of macrosomia, shoulder dystocia, preeclampsia, and neonatal hypoglycemia compared with no treatment.

However, these trials enrolled women screened at the standard window. For early-onset GDM (diagnosed before 24 weeks), data are accumulating but fewer high-quality trials exist. A 2022 systematic review and meta-analysis published in the Journal of the American Medical Association suggested that early GDM screening in high-risk women is associated with improved glycemic outcomes, less neonatal hypoglycemia, and reduced birthweight, though the effect on preeclampsia was less clear. The National Institutes of Health (NIH) and the American Diabetes Association now support early screening for women with risk factors. Despite these recommendations, many clinicians still defer universal early screening pending stronger evidence. This creates a tension in clinical practice: the existing evidence strongly favors early detection for high-risk women, yet a delay in screening—even within the standard window—can still be harmful if patients miss appointments or are not systematically tested.

Barriers to Timely GDM Screening

Several factors contribute to delayed or missed GDM screening from the patient perspective. Lack of awareness about GDM symptoms (which are often absent) may lead some women to deprioritize the glucose challenge test. Fear of the glucose drink causing nausea, vomiting, or discomfort can cause reluctance or cancellation of appointments. Limited health literacy, language barriers, and competing demands—particularly for women juggling work and childcare—may result in missed prenatal visits. Additionally, socioeconomic disparities play a role: women with Medicaid or without insurance are less likely to receive timely prenatal care and recommended screenings. Cultural beliefs that minimize the importance of blood sugar testing in pregnancy can also delay screening.

Healthcare System Barriers

On the provider side, inconsistent adherence to screening guidelines contributes to delays. Some practitioners may forget to schedule the glucose test at the correct gestational age, especially when visits are spread widely apart. Others may use outdated two-step protocols that require the patient to fast and return for a longer test, reducing compliance. Laboratory errors, miscommunication, or incorrect documentation of test timing can also cause missed diagnoses. During the COVID-19 pandemic, many prenatal visits were postponed or conducted via telemedicine, leading to a documented reduction in GDM screening rates. This disruption highlighted the vulnerability of time-sensitive screening programs to broader healthcare system pressures.

Recommendations for Expectant Mothers and Healthcare Providers

For Pregnant Women: Take Ownership of Your Screening Schedule

Expectant mothers should be proactive about GDM screening. Attend all scheduled prenatal visits and confirm with your provider that the glucose challenge test is planned between 24 and 28 weeks. If you have one or more risk factors—such as obesity, family history of diabetes, previous GDM, PCOS, or being of a high-risk ethnicity—ask about early screening at your first prenatal visit or before 20 weeks. Discuss your diet and physical activity level with your clinician; maintaining a healthy weight before and during pregnancy can reduce your risk. If you experience symptoms such as extreme thirst, frequent urination, or blurred vision, notify your provider immediately, as these can be signs of hyperglycemia. Do not skip the glucose drink because of fear of nausea—providers can offer strategies to minimize discomfort (like drinking it cold or eating a small snack beforehand).

For Healthcare Providers: Implement Systematic Screening Protocols

Clinicians should adopt clear, evidence-based screening protocols. For average-risk women, universal screening using a 50-gram oral glucose challenge test (with a 1-hour venous plasma glucose threshold of 130–140 mg/dL) is recommended at 24–28 weeks. For women with risk factors, an early screen before 20 weeks or at the first visit is appropriate, using the same test or a 75-gram 2-hour oral glucose tolerance test. Practice guidelines from ACOG, the American Diabetes Association, and the World Health Organization should be followed consistently. Electronic health record reminders can flag women due for screening and identify those with risk factors who need early testing. When a patient fails the glucose challenge test, prompt referral for the confirmatory oral glucose tolerance test and initiation of treatment (diet, lifestyle, or insulin) can prevent the harms of prolonged hyperglycemia. Postpartum follow-up is also essential: women with GDM should undergo a 75-gram 2-hour OGTT at 4–12 weeks after delivery to screen for persistent glucose intolerance.

Conclusion: Timely Screening Is a Lifesaving Intervention

Delaying GDM screening is not a benign omission. The evidence clearly shows that untreated gestational diabetes—even when it emerges within the standard screening window—causes measurable harm to mothers, fetuses, and children. Preeclampsia, macrosomia, cesarean delivery, neonatal hypoglycemia, and lifelong metabolic risks for the offspring are all increased when screening is deferred. Conversely, timely diagnosis followed by appropriate glycemic management reduces these risks and improves outcomes. Both patients and healthcare providers share responsibility for ensuring that GDM screening occurs as recommended. With the twin burdens of rising GDM prevalence and continued disparities in prenatal care access, we cannot afford to let screening fall through the cracks. An investment in timely detection is an investment in the health of two generations.

Additional resources for patients and clinicians: the American College of Obstetricians and Gynecologists’ Practice Bulletin No. 190 on Gestational Diabetes Mellitus; the Centers for Disease Control and Prevention’s gestational diabetes page; and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) information portal.