17:I[462708,["/_next/static/chunks/3yo3kiro3bmlp.js","/_next/static/chunks/3vr2wvd8f2efb.js","/_next/static/chunks/2vtmb68_vu-9t.js","/_next/static/chunks/2s8mt6_8wrpfo.js","/_next/static/chunks/3vkulz2i3l61y.js","/_next/static/chunks/1cqw2i1silz0i.js","/_next/static/chunks/14dbm3lm_t629.js","/_next/static/chunks/335_v2mb569ld.js","/_next/static/chunks/3ykn5ops9bft5.js","/_next/static/chunks/3cmavum774kjt.js","/_next/static/chunks/3th-0-a2xf9qs.js","/_next/static/chunks/0p0xpwde6kzmv.js","/_next/static/chunks/401-sxxnzbtf_.js","/_next/static/chunks/0wywtv698a1v0.js","/_next/static/chunks/2botzqwpnrzyj.js"],"ArticleReader"] 18:T527e,## Summary Gestational diabetes mellitus (GDM) is hyperglycemia first diagnosed in the second or third trimester that was not clearly overt diabetes before pregnancy. It results from pregnancy-related insulin resistance exceeding pancreatic beta-cell compensatory capacity. Maternal glucose crosses the placenta; maternal insulin does not. Fetal hyperglycemia therefore drives fetal hyperinsulinemia, excessive growth, neonatal hypoglycemia, and other metabolic complications. [1,2] Screening is generally performed at **24–28 weeks** in people not already identified as having diabetes. Diagnostic systems differ. In the one-step 75-g oral glucose tolerance test (OGTT), GDM is diagnosed if **one or more** values meet or exceed fasting **92 mg/dL (5.1 mmol/L)**, 1-hour **180 mg/dL (10.0 mmol/L)**, or 2-hour **153 mg/dL (8.5 mmol/L)**. In the U.S. two-step strategy, an abnormal 50-g screening test is followed by a fasting 100-g OGTT; Carpenter-Coustan thresholds are **95/180/155/140 mg/dL** at fasting/1/2/3 hours, with the diagnostic rule set by the governing protocol. [2,3] After diagnosis, start individualized nutrition therapy, physical activity when obstetrically safe, and glucose self-monitoring. ADA 2026 targets are fasting **<95 mg/dL (5.3 mmol/L)**, 1-hour postprandial **<140 mg/dL (7.8 mmol/L)**, or 2-hour postprandial **<120 mg/dL (6.7 mmol/L)**. For insulin-treated pregnancy, ADA lists target ranges of fasting **70–95**, 1-hour **110–140**, and 2-hour **100–120 mg/dL**, individualized to avoid clinically important hypoglycemia. [1] **Insulin is the ADA-preferred pharmacologic therapy** when lifestyle measures do not achieve targets. Metformin and glyburide cross the placenta and are not first-line agents under ADA guidance. [1] Practice differs internationally: NICE recommends metformin when diet and exercise have not achieved glucose targets within 1–2 weeks, with insulin when metformin is unsuitable or insufficient. [4] Management should therefore document which guideline framework is being used. The major maternal and fetal hazards are preeclampsia, excessive fetal growth, shoulder dystocia and birth trauma, neonatal hypoglycemia, and persistent maternal dysglycemia after pregnancy. Most GDM medication is stopped after placental delivery. Perform a **75-g OGTT 4–12 weeks postpartum** using nonpregnant criteria and continue diabetes screening every **1–3 years** thereafter. [1] > **Caution:** Marked hyperglycemia, vomiting, dehydration, abdominal pain, tachypnea, or ketones in pregnancy requires urgent assessment for diabetic ketoacidosis. Ketoacidosis can occur at lower glucose concentrations in pregnancy than outside pregnancy. ## Pathophysiology Placental hormones and maternal metabolic changes progressively increase insulin resistance, particularly in the second and third trimesters. In normal pregnancy, pancreatic beta cells increase insulin secretion enough to preserve physiologic glucose levels. GDM develops when that compensatory response is inadequate. Maternal glucose readily crosses the placenta. Fetal pancreatic insulin secretion rises in response to maternal hyperglycemia. Fetal insulin promotes adiposity and growth and contributes to: - large-for-gestational-age (LGA) birth and macrosomia; - shoulder dystocia and birth trauma; - neonatal hypoglycemia after the maternal glucose supply ends at delivery; - polycythemia and hyperbilirubinemia; - increased respiratory morbidity. The relationship between maternal glucose and pregnancy outcomes is continuous rather than defined by a single biologic threshold, which explains meaningful differences among diagnostic systems. The HAPO study established graded associations between maternal glucose and adverse perinatal outcomes across the measured range. [5] ## Classification Distinguish GDM from preexisting diabetes because congenital-malformation risk, retinal and renal assessment, medication strategy, and fetal surveillance differ. | Category | Clinical meaning | Management implication | |---|---|---| | Overt diabetes in pregnancy | Glucose meets standard diabetes criteria, often detected early | Manage as preexisting diabetes in pregnancy | | GDM controlled with lifestyle | Targets achieved without glucose-lowering medication | Continue monitoring and obstetric risk assessment | | GDM requiring medication | Insulin or locally accepted noninsulin therapy required | More frequent glucose review and often additional fetal surveillance | | Poorly controlled GDM | Recurrent values above target despite therapy or major adherence/access barriers | Prompt escalation; reassess fetal growth and maternal complications | | GDM with major comorbidity | Hypertension, preeclampsia, fetal growth disorder, polyhydramnios, or another condition | Surveillance and birth timing follow the highest-risk condition | ## Risk factors Risk is increased by: - prior GDM; - overweight or obesity; - older maternal age; - first-degree family history of diabetes; - prior LGA or macrosomic infant; - polycystic ovary syndrome; - metabolic syndrome features; - prior unexplained adverse pregnancy outcome; - population background with high type 2 diabetes prevalence; - glucocorticoid exposure or other hyperglycemia-promoting conditions. Risk-factor lists should not replace universal screening where universal screening is the local policy. ## Screening and diagnosis ### Early pregnancy: identify preexisting diabetes At the first prenatal evaluation, determine whether diabetes may have preceded pregnancy. ADA 2026 recommends early testing for undiagnosed diabetes in people with risk factors and supports broad early assessment according to the current diagnostic framework. [2] Hyperglycemia meeting standard nonpregnant diabetes criteria should be managed as diabetes in pregnancy rather than routine GDM. Early lesser abnormalities are an evolving area. Avoid automatically applying late-pregnancy GDM criteria to every early abnormal glucose value without considering the governing guideline and the evidence on early-pregnancy treatment. ### Routine 24–28 week screening #### One-step 75-g OGTT After an overnight fast, measure fasting, 1-hour, and 2-hour plasma glucose. | Time | Threshold | |---|---:| | Fasting | **92 mg/dL (5.1 mmol/L)** | | 1 hour | **180 mg/dL (10.0 mmol/L)** | | 2 hours | **153 mg/dL (8.5 mmol/L)** | One value at or above threshold establishes GDM under the one-step IADPSG/ADA strategy. [2] #### Two-step U.S. strategy **Step A:** nonfasting 50-g glucose challenge with 1-hour plasma glucose. Practices use screening thresholds commonly ranging from **130 to 140 mg/dL**. [2,3] **Step B:** if screening is positive, perform a fasting 100-g 3-hour OGTT. | Time | Carpenter-Coustan threshold | |---|---:| | Fasting | **95 mg/dL (5.3 mmol/L)** | | 1 hour | **180 mg/dL (10.0 mmol/L)** | | 2 hours | **155 mg/dL (8.6 mmol/L)** | | 3 hours | **140 mg/dL (7.8 mmol/L)** | Traditionally, two abnormal values establish GDM in the two-step strategy. Local obstetric protocols may manage one abnormal value differently; apply one declared system consistently rather than combining thresholds from different strategies. [2,3] ### NICE 75-g OGTT NICE uses risk-factor-based testing and diagnoses GDM when either: - fasting plasma glucose is **≥5.6 mmol/L**, or - 2-hour plasma glucose is **≥7.8 mmol/L**. [4] These thresholds differ from the one-step IADPSG/ADA system. Record the diagnostic framework used. ## Initial assessment after diagnosis Clarify: - gestational age and exact diagnostic values; - prior GDM, prediabetes, or diabetes; - prepregnancy weight/BMI and weight trajectory; - prior macrosomia, shoulder dystocia, stillbirth, operative birth, or neonatal hypoglycemia; - diet, food access, meal timing, and cultural dietary pattern; - physical activity and obstetric contraindications; - medications that alter glucose, especially glucocorticoids; - hypertension or preeclampsia symptoms; - ability to obtain a glucose meter, strips, insulin, and follow-up; - fetal growth and amniotic fluid findings when available. Measure blood pressure and review routine obstetric findings. Evaluate for overt diabetes or type 1 diabetes when the phenotype is atypical, hyperglycemia is marked, or ketones are present. ## Glycemic monitoring and targets A common self-monitoring plan is: - fasting glucose each morning; - 1-hour or 2-hour glucose after each meal. Use the same postmeal interval consistently. ### ADA 2026 targets | Setting | Fasting | 1-hour postmeal | 2-hour postmeal | |---|---:|---:|---:| | GDM without insulin | **<95 mg/dL** | **<140 mg/dL** | **<120 mg/dL** | | Insulin-treated pregnancy target range | **70–95 mg/dL** | **110–140 mg/dL** | **100–120 mg/dL** | Targets may require individualization when recurrent hypoglycemia prevents safe achievement. [1] ### Pattern-based response | Pattern | Likely next action | |---|---| | Fasting repeatedly above target; postmeal values controlled | Review evening intake and sleep; add or titrate basal insulin if persistent | | One meal repeatedly high | Adjust that meal and/or use meal-specific rapid-acting insulin | | Most postmeal values high | Review carbohydrate distribution; consider prandial insulin | | Fasting and postmeal values high | Basal-bolus strategy may be needed | | Erratic readings | Verify timing, hand washing, meter technique, diet, adherence, access, and steroid exposure | | Recurrent hypoglycemia | Reduce therapy and reassess intake, timing, and dose | | Unexpected fall in insulin needs late in pregnancy | Assess intake and dosing error; consider obstetric/placental context if clinically concerning | ## Nutrition therapy Individualized medical nutrition therapy is first-line for most GDM. [1] Goals are adequate pregnancy nutrition, appropriate gestational weight gain, and reduction of postprandial glucose excursions without severe carbohydrate restriction. Practical principles: - distribute carbohydrate across meals and snacks; - favor high-fiber, minimally processed carbohydrate sources; - pair carbohydrate with protein and unsaturated fat; - limit sugar-sweetened beverages and highly refined carbohydrate; - avoid ketogenic or markedly carbohydrate-restricted diets; - adjust meal-specific carbohydrate based on glucose patterns. ADA cites pregnancy dietary reference intakes of at least **175 g carbohydrate/day, 71 g protein/day, and 28 g fiber/day**. [1] Dietitian referral is particularly useful when glucose patterns are complex, food insecurity is present, cultural dietary adaptation is needed, or multiple food restrictions are developing. ## Physical activity For pregnant people without an obstetric contraindication, regular moderate activity improves insulin sensitivity. ADA supports approximately **150 minutes per week** of moderate-intensity aerobic activity, distributed through the week. [1] Short postmeal walks can be useful for postprandial glucose control. Modify activity for obstetric complications such as significant bleeding, ruptured membranes, threatened preterm birth, or hemodynamically important disease. ## Pharmacologic therapy Add medication when glucose remains above target despite a feasible trial of nutrition and activity, or earlier when hyperglycemia is substantial and delay is inappropriate. ### Insulin Insulin is preferred by ADA because it does not cross the placenta and can be matched to the glucose pattern. [1] Common components include: - rapid-acting insulin lispro or aspart for meal-related hyperglycemia; - basal NPH or a long-acting insulin with established pregnancy use, selected according to local protocol. Dose is individualized to body size, gestational stage, glucose pattern, diet, and hypoglycemia risk. Pregnancy insulin needs can change rapidly; titration should be based on serial glucose data rather than a fixed dose formula. Teach: - injection technique and storage; - hypoglycemia recognition and treatment; - meal timing; - sick-day and ketone guidance; - when to seek urgent care. ### Metformin ADA 2026 does not recommend metformin as first-line GDM pharmacotherapy because it crosses the placenta and may not achieve glycemic targets in all patients. [1] NICE takes a different approach: when diet and activity have not achieved targets within **1–2 weeks**, metformin is offered if suitable, with insulin when metformin is contraindicated, unacceptable, or insufficient. [4] Where metformin is used, review renal function, gastrointestinal adverse effects, placental transfer, and the possibility that supplemental insulin will still be required. ### Glyburide Glyburide is not a preferred first-line agent under ADA guidance because it crosses the placenta and has concerns regarding treatment failure and neonatal outcomes. [1] ### Other glucose-lowering medicines GLP-1 receptor agonists, SGLT2 inhibitors, DPP-4 inhibitors, and most other noninsulin agents are not routine GDM treatment because pregnancy safety and efficacy data are inadequate. ## Maternal and fetal surveillance At each review, assess: - fasting and postmeal trends; - hypoglycemia; - nutrition and weight trajectory; - blood pressure and preeclampsia symptoms; - medication adherence and access; - fetal growth information; - amniotic fluid when assessed; - new steroid exposure or acute illness. ### Fetal growth Ultrasound growth assessment is used according to local obstetric policy. Estimated fetal weight has meaningful error, so decisions about birth route should integrate the overall obstetric history, growth trajectory, prior shoulder dystocia, glucose control, and patient preference. ### Antenatal fetal surveillance ACOG guidance notes that patients with diet-controlled GDM and no other comorbidity may not require routine testing before 40 weeks, whereas once- or twice-weekly surveillance from around **32 weeks** may be considered for medication-controlled GDM; poorly controlled disease may warrant at least twice-weekly surveillance and earlier individualized assessment. [6] Surveillance does not replace treatment of hyperglycemia or response to maternal deterioration. ## Birth planning Timing of birth depends on: - lifestyle-controlled versus medication-treated disease; - quality and stability of glucose control; - fetal growth and amniotic fluid; - hypertension or preeclampsia; - prior obstetric history; - local guideline. NICE recommends that uncomplicated GDM pregnancies proceed to birth no later than **40 weeks + 6 days**, with earlier birth when maternal or fetal complications are present. [4] U.S. institutions use stratified obstetric protocols; follow the current local standard rather than one gestational-age rule for every patient. GDM alone is not an indication for cesarean birth. Route of birth is based on standard obstetric indications plus fetal size, prior shoulder dystocia, and individualized risk. ### Intrapartum glucose Avoid marked maternal hyperglycemia while preventing hypoglycemia. NICE uses a target of **4–7 mmol/L** during labor and birth for women with diabetes. [4] Follow the institution's insulin/dextrose protocol when medication is required. ## Neonatal care Communicate the maternal GDM history to the neonatal team, particularly when medication was required or glucose control was poor. Neonatal risks include: - hypoglycemia; - respiratory morbidity; - hyperbilirubinemia; - polycythemia; - feeding problems; - birth trauma after excessive fetal growth. Early feeding and neonatal glucose monitoring should follow local neonatal guidance. ## Postpartum care ### Immediately after delivery Placental delivery rapidly reduces insulin resistance. Most patients with GDM can stop pregnancy glucose-lowering therapy after birth. Continue treatment only when persistent hyperglycemia or preexisting diabetes requires it. Provide a postpartum testing plan before discharge. ### 4–12 weeks postpartum ADA recommends a fasting **75-g 2-hour OGTT** at 4–12 weeks using nonpregnant criteria. [1] The OGTT is preferred over A1C in this early period because pregnancy-related red-cell turnover and delivery blood loss can distort A1C and because OGTT is more sensitive for impaired glucose tolerance. | Category | Fasting plasma glucose | 2-hour 75-g OGTT | |---|---:|---:| | Normal | <100 mg/dL | <140 mg/dL | | Prediabetes | 100–125 mg/dL | 140–199 mg/dL | | Diabetes | ≥126 mg/dL | ≥200 mg/dL | In the absence of unequivocal hyperglycemia, confirm diabetes according to standard diagnostic rules. [2] ### Long-term prevention After a normal postpartum OGTT, repeat diabetes screening every **1–3 years**. [1] Prior GDM is a strong marker of future type 2 diabetes risk. Weight management, physical activity, healthy dietary pattern, and treatment of prediabetes are part of long-term care. Screen before a future pregnancy whenever possible. ## Special situations ### Prior bariatric surgery A standard glucose load can cause dumping or reactive hypoglycemia after some bariatric procedures. Coordinate with maternal-fetal medicine or endocrinology; alternative capillary glucose or continuous glucose monitoring strategies may be used locally, although they are not identical to a validated OGTT pathway. ### Antenatal corticosteroids Corticosteroids can cause substantial transient hyperglycemia. Patients using insulin often need temporary dose increases and closer monitoring. ### Suspected type 1 diabetes Marked hyperglycemia, ketones, weight loss, or rapidly progressive insulin dependence should prompt assessment for type 1 diabetes. Do not assume all hyperglycemia first recognized during pregnancy is GDM. ### Fasting Prolonged fasting may increase maternal hypoglycemia, dehydration, and ketosis risk. Provide individualized counseling and adjust medication and monitoring when a patient chooses to fast. ## Acute deterioration checklist For an unwell pregnant patient with GDM: - check vital signs and obstetric status; - measure bedside glucose; - check blood or urine ketones when vomiting, dehydrated, tachypneic, or markedly hyperglycemic; - obtain electrolytes and acid-base testing when ketoacidosis is possible; - assess for infection and preeclampsia; - review recent corticosteroids and missed insulin; - assess fetal status when gestational age and clinical context warrant; - treat hypoglycemia promptly; - escalate to obstetrics, endocrinology, and critical care for ketoacidosis, severe hypertension, fetal compromise, or inability to maintain hydration. ## Related library topics - [Type 2 Diabetes Mellitus](../endocrinology/type-2-diabetes-mellitus.md) - [Type 1 Diabetes Mellitus in Adults](../endocrinology/type-1-diabetes-mellitus-in-adults.md) - [Diabetic Ketoacidosis](../endocrinology/diabetic-ketoacidosis.md) - [Preeclampsia and Eclampsia](preeclampsia-and-eclampsia.md) - [Polycystic Ovary Syndrome](../endocrinology/polycystic-ovary-syndrome.md) ## References 1. American Diabetes Association Professional Practice Committee for Diabetes. 15. Management of Diabetes in Pregnancy: Standards of Care in Diabetes—2026. *Diabetes Care.* 2026;49(Suppl 1):S321-S338. DOI: 10.2337/dc26-S015. PMID: 41358885. https://diabetesjournals.org/care/article/49/Supplement_1/S321/163918/ 2. American Diabetes Association Professional Practice Committee for Diabetes. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2026. *Diabetes Care.* 2026;49(Suppl 1):S27-S49. DOI: 10.2337/dc26-S002. PMID: 41358893. 3. U.S. Preventive Services Task Force. Gestational Diabetes: Screening. Final Recommendation Statement. August 10, 2021. https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/gestational-diabetes-screening 4. National Institute for Health and Care Excellence. Diabetes in pregnancy: management from preconception to the postnatal period (NG3). Published 2015; last updated December 16, 2020; reviewed April 30, 2025. https://www.nice.org.uk/guidance/ng3/chapter/recommendations 5. HAPO Study Cooperative Research Group. Hyperglycemia and adverse pregnancy outcomes. *N Engl J Med.* 2008;358:1991-2002. DOI: 10.1056/NEJMoa0707943. PMID: 18463375. 6. American College of Obstetricians and Gynecologists. Indications for Outpatient Antenatal Fetal Surveillance. Committee Opinion No. 828. 2021. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2021/06/indications-for-outpatient-antenatal-fetal-surveillance 7. Crowther CA, Hiller JE, Moss JR, et al. Effect of treatment of gestational diabetes mellitus on pregnancy outcomes. *N Engl J Med.* 2005;352:2477-2486. DOI: 10.1056/NEJMoa042973. PMID: 15951574. 8. Landon MB, Spong CY, Thom E, et al. A multicenter, randomized trial of treatment for mild gestational diabetes. *N Engl J Med.* 2009;361:1339-1348. DOI: 10.1056/NEJMoa0902430. PMID: 19797280. 9. Simmons D, Immanuel J, Hague WM, et al. Treatment of Gestational Diabetes Mellitus Diagnosed Early in Pregnancy. *N Engl J Med.* 2023;388:2132-2144. DOI: 10.1056/NEJMoa2214956.19:T52a0,## Summary Gestational diabetes mellitus (GDM) is hyperglycemia first diagnosed in the second or third trimester that was not clearly overt diabetes before pregnancy. It results from pregnancy-related insulin resistance exceeding pancreatic beta-cell compensatory capacity. Maternal glucose crosses the placenta; maternal insulin does not. Fetal hyperglycemia therefore drives fetal hyperinsulinemia, excessive growth, neonatal hypoglycemia, and other metabolic complications. [1,2] Screening is generally performed at **24–28 weeks** in people not already identified as having diabetes. Diagnostic systems differ. In the one-step 75-g oral glucose tolerance test (OGTT), GDM is diagnosed if **one or more** values meet or exceed fasting **92 mg/dL (5.1 mmol/L)**, 1-hour **180 mg/dL (10.0 mmol/L)**, or 2-hour **153 mg/dL (8.5 mmol/L)**. In the U.S. two-step strategy, an abnormal 50-g screening test is followed by a fasting 100-g OGTT; Carpenter-Coustan thresholds are **95/180/155/140 mg/dL** at fasting/1/2/3 hours, with the diagnostic rule set by the governing protocol. [2,3] After diagnosis, start individualized nutrition therapy, physical activity when obstetrically safe, and glucose self-monitoring. ADA 2026 targets are fasting **<95 mg/dL (5.3 mmol/L)**, 1-hour postprandial **<140 mg/dL (7.8 mmol/L)**, or 2-hour postprandial **<120 mg/dL (6.7 mmol/L)**. For insulin-treated pregnancy, ADA lists target ranges of fasting **70–95**, 1-hour **110–140**, and 2-hour **100–120 mg/dL**, individualized to avoid clinically important hypoglycemia. [1] **Insulin is the ADA-preferred pharmacologic therapy** when lifestyle measures do not achieve targets. Metformin and glyburide cross the placenta and are not first-line agents under ADA guidance. [1] Practice differs internationally: NICE recommends metformin when diet and exercise have not achieved glucose targets within 1–2 weeks, with insulin when metformin is unsuitable or insufficient. [4] Management should therefore document which guideline framework is being used. The major maternal and fetal hazards are preeclampsia, excessive fetal growth, shoulder dystocia and birth trauma, neonatal hypoglycemia, and persistent maternal dysglycemia after pregnancy. Most GDM medication is stopped after placental delivery. Perform a **75-g OGTT 4–12 weeks postpartum** using nonpregnant criteria and continue diabetes screening every **1–3 years** thereafter. [1] > **Caution:** Marked hyperglycemia, vomiting, dehydration, abdominal pain, tachypnea, or ketones in pregnancy requires urgent assessment for [diabetic ketoacidosis](/library/diabetic-ketoacidosis). Ketoacidosis can occur at lower glucose concentrations in pregnancy than outside pregnancy. ## Pathophysiology Placental hormones and maternal metabolic changes progressively increase insulin resistance, particularly in the second and third trimesters. In normal pregnancy, pancreatic beta cells increase insulin secretion enough to preserve physiologic glucose levels. GDM develops when that compensatory response is inadequate. Maternal glucose readily crosses the placenta. Fetal pancreatic insulin secretion rises in response to maternal hyperglycemia. Fetal insulin promotes adiposity and growth and contributes to: - large-for-gestational-age (LGA) birth and macrosomia; - shoulder dystocia and birth trauma; - neonatal hypoglycemia after the maternal glucose supply ends at delivery; - polycythemia and hyperbilirubinemia; - increased respiratory morbidity. The relationship between maternal glucose and pregnancy outcomes is continuous rather than defined by a single biologic threshold, which explains meaningful differences among diagnostic systems. The HAPO study established graded associations between maternal glucose and adverse perinatal outcomes across the measured range. [5] ## Classification Distinguish GDM from preexisting diabetes because congenital-malformation risk, retinal and renal assessment, medication strategy, and fetal surveillance differ. | Category | Clinical meaning | Management implication | |---|---|---| | Overt diabetes in pregnancy | Glucose meets standard diabetes criteria, often detected early | Manage as preexisting diabetes in pregnancy | | GDM controlled with lifestyle | Targets achieved without glucose-lowering medication | Continue monitoring and obstetric risk assessment | | GDM requiring medication | Insulin or locally accepted noninsulin therapy required | More frequent glucose review and often additional fetal surveillance | | Poorly controlled GDM | Recurrent values above target despite therapy or major adherence/access barriers | Prompt escalation; reassess fetal growth and maternal complications | | GDM with major comorbidity | Hypertension, preeclampsia, fetal growth disorder, polyhydramnios, or another condition | Surveillance and birth timing follow the highest-risk condition | ## Risk factors Risk is increased by: - prior GDM; - overweight or obesity; - older maternal age; - first-degree family history of diabetes; - prior LGA or macrosomic infant; - polycystic ovary syndrome; - metabolic syndrome features; - prior unexplained adverse pregnancy outcome; - population background with high type 2 diabetes prevalence; - glucocorticoid exposure or other hyperglycemia-promoting conditions. Risk-factor lists should not replace universal screening where universal screening is the local policy. ## Screening and diagnosis ### Early pregnancy: identify preexisting diabetes At the first prenatal evaluation, determine whether diabetes may have preceded pregnancy. ADA 2026 recommends early testing for undiagnosed diabetes in people with risk factors and supports broad early assessment according to the current diagnostic framework. [2] Hyperglycemia meeting standard nonpregnant diabetes criteria should be managed as diabetes in pregnancy rather than routine GDM. Early lesser abnormalities are an evolving area. Avoid automatically applying late-pregnancy GDM criteria to every early abnormal glucose value without considering the governing guideline and the evidence on early-pregnancy treatment. ### Routine 24–28 week screening #### One-step 75-g OGTT After an overnight fast, measure fasting, 1-hour, and 2-hour plasma glucose. | Time | Threshold | |---|---:| | Fasting | **92 mg/dL (5.1 mmol/L)** | | 1 hour | **180 mg/dL (10.0 mmol/L)** | | 2 hours | **153 mg/dL (8.5 mmol/L)** | One value at or above threshold establishes GDM under the one-step IADPSG/ADA strategy. [2] #### Two-step U.S. strategy **Step A:** nonfasting 50-g glucose challenge with 1-hour plasma glucose. Practices use screening thresholds commonly ranging from **130 to 140 mg/dL**. [2,3] **Step B:** if screening is positive, perform a fasting 100-g 3-hour OGTT. | Time | Carpenter-Coustan threshold | |---|---:| | Fasting | **95 mg/dL (5.3 mmol/L)** | | 1 hour | **180 mg/dL (10.0 mmol/L)** | | 2 hours | **155 mg/dL (8.6 mmol/L)** | | 3 hours | **140 mg/dL (7.8 mmol/L)** | Traditionally, two abnormal values establish GDM in the two-step strategy. Local obstetric protocols may manage one abnormal value differently; apply one declared system consistently rather than combining thresholds from different strategies. [2,3] ### NICE 75-g OGTT NICE uses risk-factor-based testing and diagnoses GDM when either: - fasting plasma glucose is **≥5.6 mmol/L**, or - 2-hour plasma glucose is **≥7.8 mmol/L**. [4] These thresholds differ from the one-step IADPSG/ADA system. Record the diagnostic framework used. ## Initial assessment after diagnosis Clarify: - gestational age and exact diagnostic values; - prior GDM, prediabetes, or diabetes; - prepregnancy weight/BMI and weight trajectory; - prior macrosomia, shoulder dystocia, stillbirth, operative birth, or neonatal hypoglycemia; - diet, food access, meal timing, and cultural dietary pattern; - physical activity and obstetric contraindications; - medications that alter glucose, especially glucocorticoids; - hypertension or preeclampsia symptoms; - ability to obtain a glucose meter, strips, insulin, and follow-up; - fetal growth and amniotic fluid findings when available. Measure blood pressure and review routine obstetric findings. Evaluate for overt diabetes or type 1 diabetes when the phenotype is atypical, hyperglycemia is marked, or ketones are present. ## Glycemic monitoring and targets A common self-monitoring plan is: - fasting glucose each morning; - 1-hour or 2-hour glucose after each meal. Use the same postmeal interval consistently. ### ADA 2026 targets | Setting | Fasting | 1-hour postmeal | 2-hour postmeal | |---|---:|---:|---:| | GDM without insulin | **<95 mg/dL** | **<140 mg/dL** | **<120 mg/dL** | | Insulin-treated pregnancy target range | **70–95 mg/dL** | **110–140 mg/dL** | **100–120 mg/dL** | Targets may require individualization when recurrent hypoglycemia prevents safe achievement. [1] ### Pattern-based response | Pattern | Likely next action | |---|---| | Fasting repeatedly above target; postmeal values controlled | Review evening intake and sleep; add or titrate basal insulin if persistent | | One meal repeatedly high | Adjust that meal and/or use meal-specific rapid-acting insulin | | Most postmeal values high | Review carbohydrate distribution; consider prandial insulin | | Fasting and postmeal values high | Basal-bolus strategy may be needed | | Erratic readings | Verify timing, hand washing, meter technique, diet, adherence, access, and steroid exposure | | Recurrent hypoglycemia | Reduce therapy and reassess intake, timing, and dose | | Unexpected fall in insulin needs late in pregnancy | Assess intake and dosing error; consider obstetric/placental context if clinically concerning | ## Nutrition therapy Individualized medical nutrition therapy is first-line for most GDM. [1] Goals are adequate pregnancy nutrition, appropriate gestational weight gain, and reduction of postprandial glucose excursions without severe carbohydrate restriction. Practical principles: - distribute carbohydrate across meals and snacks; - favor high-fiber, minimally processed carbohydrate sources; - pair carbohydrate with protein and unsaturated fat; - limit sugar-sweetened beverages and highly refined carbohydrate; - avoid ketogenic or markedly carbohydrate-restricted diets; - adjust meal-specific carbohydrate based on glucose patterns. ADA cites pregnancy dietary reference intakes of at least **175 g carbohydrate/day, 71 g protein/day, and 28 g fiber/day**. [1] Dietitian referral is particularly useful when glucose patterns are complex, food insecurity is present, cultural dietary adaptation is needed, or multiple food restrictions are developing. ## Physical activity For pregnant people without an obstetric contraindication, regular moderate activity improves insulin sensitivity. ADA supports approximately **150 minutes per week** of moderate-intensity aerobic activity, distributed through the week. [1] Short postmeal walks can be useful for postprandial glucose control. Modify activity for obstetric complications such as significant bleeding, ruptured membranes, threatened preterm birth, or hemodynamically important disease. ## Pharmacologic therapy Add medication when glucose remains above target despite a feasible trial of nutrition and activity, or earlier when hyperglycemia is substantial and delay is inappropriate. ### Insulin Insulin is preferred by ADA because it does not cross the placenta and can be matched to the glucose pattern. [1] Common components include: - rapid-acting insulin lispro or aspart for meal-related hyperglycemia; - basal NPH or a long-acting insulin with established pregnancy use, selected according to local protocol. Dose is individualized to body size, gestational stage, glucose pattern, diet, and hypoglycemia risk. Pregnancy insulin needs can change rapidly; titration should be based on serial glucose data rather than a fixed dose formula. Teach: - injection technique and storage; - hypoglycemia recognition and treatment; - meal timing; - sick-day and ketone guidance; - when to seek urgent care. ### Metformin ADA 2026 does not recommend metformin as first-line GDM pharmacotherapy because it crosses the placenta and may not achieve glycemic targets in all patients. [1] NICE takes a different approach: when diet and activity have not achieved targets within **1–2 weeks**, metformin is offered if suitable, with insulin when metformin is contraindicated, unacceptable, or insufficient. [4] Where metformin is used, review renal function, gastrointestinal adverse effects, placental transfer, and the possibility that supplemental insulin will still be required. ### Glyburide Glyburide is not a preferred first-line agent under ADA guidance because it crosses the placenta and has concerns regarding treatment failure and neonatal outcomes. [1] ### Other glucose-lowering medicines GLP-1 receptor agonists, SGLT2 inhibitors, DPP-4 inhibitors, and most other noninsulin agents are not routine GDM treatment because pregnancy safety and efficacy data are inadequate. ## Maternal and fetal surveillance At each review, assess: - fasting and postmeal trends; - hypoglycemia; - nutrition and weight trajectory; - blood pressure and preeclampsia symptoms; - medication adherence and access; - fetal growth information; - amniotic fluid when assessed; - new steroid exposure or acute illness. ### Fetal growth Ultrasound growth assessment is used according to local obstetric policy. Estimated fetal weight has meaningful error, so decisions about birth route should integrate the overall obstetric history, growth trajectory, prior shoulder dystocia, glucose control, and patient preference. ### Antenatal fetal surveillance ACOG guidance notes that patients with diet-controlled GDM and no other comorbidity may not require routine testing before 40 weeks, whereas once- or twice-weekly surveillance from around **32 weeks** may be considered for medication-controlled GDM; poorly controlled disease may warrant at least twice-weekly surveillance and earlier individualized assessment. [6] Surveillance does not replace treatment of hyperglycemia or response to maternal deterioration. ## Birth planning Timing of birth depends on: - lifestyle-controlled versus medication-treated disease; - quality and stability of glucose control; - fetal growth and amniotic fluid; - hypertension or preeclampsia; - prior obstetric history; - local guideline. NICE recommends that uncomplicated GDM pregnancies proceed to birth no later than **40 weeks + 6 days**, with earlier birth when maternal or fetal complications are present. [4] U.S. institutions use stratified obstetric protocols; follow the current local standard rather than one gestational-age rule for every patient. GDM alone is not an indication for cesarean birth. Route of birth is based on standard obstetric indications plus fetal size, prior shoulder dystocia, and individualized risk. ### Intrapartum glucose Avoid marked maternal hyperglycemia while preventing hypoglycemia. NICE uses a target of **4–7 mmol/L** during labor and birth for women with diabetes. [4] Follow the institution's insulin/dextrose protocol when medication is required. ## Neonatal care Communicate the maternal GDM history to the neonatal team, particularly when medication was required or glucose control was poor. Neonatal risks include: - hypoglycemia; - respiratory morbidity; - hyperbilirubinemia; - polycythemia; - feeding problems; - birth trauma after excessive fetal growth. Early feeding and neonatal glucose monitoring should follow local neonatal guidance. ## Postpartum care ### Immediately after delivery Placental delivery rapidly reduces insulin resistance. Most patients with GDM can stop pregnancy glucose-lowering therapy after birth. Continue treatment only when persistent hyperglycemia or preexisting diabetes requires it. Provide a postpartum testing plan before discharge. ### 4–12 weeks postpartum ADA recommends a fasting **75-g 2-hour OGTT** at 4–12 weeks using nonpregnant criteria. [1] The OGTT is preferred over A1C in this early period because pregnancy-related red-cell turnover and delivery blood loss can distort A1C and because OGTT is more sensitive for impaired glucose tolerance. | Category | Fasting plasma glucose | 2-hour 75-g OGTT | |---|---:|---:| | Normal | <100 mg/dL | <140 mg/dL | | Prediabetes | 100–125 mg/dL | 140–199 mg/dL | | Diabetes | ≥126 mg/dL | ≥200 mg/dL | In the absence of unequivocal hyperglycemia, confirm diabetes according to standard diagnostic rules. [2] ### Long-term prevention After a normal postpartum OGTT, repeat diabetes screening every **1–3 years**. [1] Prior GDM is a strong marker of future type 2 diabetes risk. Weight management, physical activity, healthy dietary pattern, and treatment of prediabetes are part of long-term care. Screen before a future pregnancy whenever possible. ## Special situations ### Prior bariatric surgery A standard glucose load can cause dumping or reactive hypoglycemia after some bariatric procedures. Coordinate with maternal-fetal medicine or endocrinology; alternative capillary glucose or continuous glucose monitoring strategies may be used locally, although they are not identical to a validated OGTT pathway. ### Antenatal corticosteroids Corticosteroids can cause substantial transient hyperglycemia. Patients using insulin often need temporary dose increases and closer monitoring. ### Suspected type 1 diabetes Marked hyperglycemia, ketones, weight loss, or rapidly progressive insulin dependence should prompt assessment for type 1 diabetes. Do not assume all hyperglycemia first recognized during pregnancy is GDM. ### Fasting Prolonged fasting may increase maternal hypoglycemia, dehydration, and ketosis risk. Provide individualized counseling and adjust medication and monitoring when a patient chooses to fast. ## Acute deterioration checklist For an unwell pregnant patient with GDM: - check vital signs and obstetric status; - measure bedside glucose; - check blood or urine ketones when vomiting, dehydrated, tachypneic, or markedly hyperglycemic; - obtain electrolytes and acid-base testing when ketoacidosis is possible; - assess for infection and preeclampsia; - review recent corticosteroids and missed insulin; - assess fetal status when gestational age and clinical context warrant; - treat hypoglycemia promptly; - escalate to obstetrics, endocrinology, and critical care for ketoacidosis, severe hypertension, fetal compromise, or inability to maintain hydration. ## Related library topics - [Type 2 Diabetes Mellitus](../endocrinology/type-2-diabetes-mellitus.md) - [Type 1 Diabetes Mellitus in Adults](../endocrinology/type-1-diabetes-mellitus-in-adults.md) - [Diabetic Ketoacidosis](../endocrinology/diabetic-ketoacidosis.md) - [Preeclampsia and Eclampsia](preeclampsia-and-eclampsia.md) - [Polycystic Ovary Syndrome](../endocrinology/polycystic-ovary-syndrome.md) ## References 1. American Diabetes Association Professional Practice Committee for Diabetes. 15. Management of Diabetes in Pregnancy: Standards of Care in Diabetes—2026. *Diabetes Care.* 2026;49(Suppl 1):S321-S338. DOI: 10.2337/dc26-S015. PMID: 41358885. https://diabetesjournals.org/care/article/49/Supplement_1/S321/163918/ 2. American Diabetes Association Professional Practice Committee for Diabetes. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2026. *Diabetes Care.* 2026;49(Suppl 1):S27-S49. DOI: 10.2337/dc26-S002. PMID: 41358893. 3. U.S. Preventive Services Task Force. Gestational Diabetes: Screening. Final Recommendation Statement. August 10, 2021. https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/gestational-diabetes-screening 4. National Institute for Health and Care Excellence. Diabetes in pregnancy: management from preconception to the postnatal period (NG3). Published 2015; last updated December 16, 2020; reviewed April 30, 2025. https://www.nice.org.uk/guidance/ng3/chapter/recommendations 5. HAPO Study Cooperative Research Group. Hyperglycemia and adverse pregnancy outcomes. *N Engl J Med.* 2008;358:1991-2002. DOI: 10.1056/NEJMoa0707943. PMID: 18463375. 6. American College of Obstetricians and Gynecologists. Indications for Outpatient Antenatal Fetal Surveillance. Committee Opinion No. 828. 2021. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2021/06/indications-for-outpatient-antenatal-fetal-surveillance 7. Crowther CA, Hiller JE, Moss JR, et al. Effect of treatment of gestational diabetes mellitus on pregnancy outcomes. *N Engl J Med.* 2005;352:2477-2486. DOI: 10.1056/NEJMoa042973. PMID: 15951574. 8. Landon MB, Spong CY, Thom E, et al. A multicenter, randomized trial of treatment for mild gestational diabetes. *N Engl J Med.* 2009;361:1339-1348. DOI: 10.1056/NEJMoa0902430. PMID: 19797280. 9. Simmons D, Immanuel J, Hague WM, et al. Treatment of Gestational Diabetes Mellitus Diagnosed Early in Pregnancy. *N Engl J Med.* 2023;388:2132-2144. DOI: 10.1056/NEJMoa2214956.7:["$","$L17",null,{"article":{"id":"medical-gestational-diabetes-mellitus","title":"Gestational Diabetes Mellitus","slug":"gestational-diabetes-mellitus","description":"Gestational diabetes mellitus (GDM) is hyperglycemia first diagnosed in the second or third trimester that was not clearly overt diabetes before pregnancy. 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