Reproductive · Year 2 · from Reproductive
Case 2: Gestational Diabetes Mellitus
Clinical Image
Source: Wikipedia - Gestational diabetes - CC BY-SA 3.0
Case Presentation
A 33-year-old G2P1 at 26 weeks gestation presents for routine prenatal care. Her first pregnancy 3 years ago was complicated by gestational diabetes controlled with diet. Her pre-pregnancy BMI is 31 and she has a family history of type 2 diabetes in her mother. Given her history, she underwent early glucose screening at her first prenatal visit, which was normal. At 24 weeks, she completed a 50-gram glucose challenge test with a 1-hour glucose of 162 mg/dL (elevated). She then completed a 100-gram oral glucose tolerance test with results: fasting 98 mg/dL, 1-hour 192 mg/dL, 2-hour 168 mg/dL, 3-hour 145 mg/dL. With three abnormal values (fasting >95, 1-hour >180, 2-hour >155, 3-hour >140), the diagnosis of gestational diabetes mellitus is confirmed. She is referred to a diabetes educator and registered dietitian for medical nutrition therapy and glucose self-monitoring instruction. Her target glucose values are fasting <95 mg/dL and 1-hour postprandial <140 mg/dL. After 2 weeks of dietary management, her fasting values remain elevated at 105-115 mg/dL despite compliance. Bedtime NPH insulin is initiated. Her postprandial values are well-controlled with diet alone. Growth ultrasounds are performed, showing appropriate fetal growth. She undergoes successful induction of labor at 39 weeks and delivers a healthy 3.6 kg infant. Postpartum glucose tolerance testing at 6-12 weeks is planned to screen for persistent diabetes.
Key Learning Points
- Gestational diabetes reflects inadequate insulin secretion to overcome the insulin resistance of pregnancy; screening is universal at 24-28 weeks, with earlier screening for high-risk women
- The two-step approach uses a 50g glucose challenge test followed by a 100g OGTT if screening is abnormal; GDM is diagnosed with 2 or more elevated values
- Medical nutrition therapy is first-line; insulin is added when diet fails to achieve targets (fasting <95, 1-hour postprandial <140, 2-hour postprandial <120 mg/dL)
- Complications include fetal macrosomia, birth injury (shoulder dystocia), neonatal hypoglycemia, and substantially increased risk of maternal type 2 diabetes postpartum