About This Page
This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Screen most pregnant patients for GDM at 24-28 weeks; screen earlier for overt diabetes if high-risk
- US standard: 50-g 1-hour glucose challenge followed by 100-g 3-hour OGTT if abnormal
- First-line treatment is nutrition therapy, exercise, and home glucose monitoring
- Insulin is preferred medication when lifestyle therapy fails
- Postpartum 75-g OGTT at 4-12 weeks is required
Overview
Gestational diabetes mellitus is carbohydrate intolerance first recognized during pregnancy. Placental hormones cause progressive insulin resistance, especially in the second and third trimesters. Poor control increases fetal hyperinsulinemia, macrosomia, shoulder dystocia, neonatal hypoglycemia, and cesarean risk.
Epidemiology
Prevalence varies by population and diagnostic criteria. Risk factors include obesity, advanced maternal age, prior GDM, prior macrosomic infant, family history of diabetes, PCOS, and high-risk ancestry. GDM strongly predicts future type 2 diabetes.
Clinical Features
Symptoms
Most patients are asymptomatic
Polyuria, polydipsia, or weight loss suggests overt diabetes
Excess fetal growth or polyhydramnios may suggest hyperglycemia
Decreased fetal movement requires immediate assessment
Preeclampsia symptoms may coexist
Signs
Fundal height greater than dates
Maternal obesity or acanthosis nigricans
Elevated home fasting/postprandial glucose values
Hypertension or proteinuria suggests preeclampsia
Large-for-gestational-age fetus on ultrasound
Investigations
First-line
50-g 1-hour glucose challengeNonfasting screen at 24-28 weeks
100-g 3-hour OGTTDiagnostic test after abnormal screen; diagnosis when at least two values exceed threshold
Home glucose monitoringFasting and postprandial values guide treatment
Second-line
Early diabetes testingHigh-risk patients can be tested early for undiagnosed type 2 diabetes
Fetal growth ultrasoundAssess estimated fetal weight and amniotic fluid
Antenatal testingUsed for medication-treated or poorly controlled GDM
Specialist
Diabetes education/nutrition consultMedical nutrition therapy and glucose log review
Maternal-fetal medicine referralPoor control, suspected macrosomia, comorbidity, or insulin intensification
Management
ACOG Practice Bulletin: Gestational Diabetes Mellitus and USPSTF Screening Recommendations1
Lifestyle and monitoring
- Medical nutrition therapy with controlled carbohydrate distribution
- Moderate exercise if no obstetric contraindication
- Self-monitor fasting and postprandial glucose
- Adjust therapy based on glucose logs
2
Pharmacologic therapy
- Start medication if targets remain elevated despite lifestyle therapy
- Insulin is preferred because it does not cross the placenta
- Metformin may be used in selected patients but crosses placenta
- Glyburide is generally less preferred due to neonatal hypoglycemia/macrosomia concerns
3
Delivery planning
- Diet-controlled well-controlled GDM: avoid delivery before 39 weeks without indication
- Medication-controlled well-controlled GDM: delivery often around 39 weeks
- Poor control may require earlier individualized delivery
- Consider cesarean if estimated fetal weight >=4500 g in diabetic pregnancy
4
Postpartum
- Stop insulin after delivery for isolated GDM unless hyperglycemia persists
- 75-g 2-hour OGTT at 4-12 weeks postpartum
- Lifelong diabetes screening every 1-3 years
- Encourage breastfeeding and weight management
Complications
- Macrosomia: Fetal hyperinsulinemia increases birth trauma risk
- Neonatal hypoglycemia: Persistent fetal insulin after cord clamping
- Polyhydramnios: Fetal osmotic diuresis
- Preeclampsia: Risk is increased
- Future diabetes: Maternal and child metabolic risk increases
USMLE Step 2 CK Exam Tips
- 1Screen at 24-28 weeks with 50-g 1-hour glucose challenge
- 2Abnormal screen → 100-g 3-hour OGTT
- 3First-line management = diet, exercise, glucose monitoring
- 4Medication after lifestyle failure = insulin preferred
- 5Mechanism: maternal hyperglycemia → fetal hyperinsulinemia → macrosomia/neonatal hypoglycemia
- 6Estimated fetal weight >=4500 g in diabetic pregnancy = consider planned cesarean
- 7Postpartum test = 75-g OGTT at 4-12 weeks
practicetest your knowledge on gestational diabetesApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — obstetrics & gynecology and beyond.
open q-bank