Screening for Gestational Diabetes at 24-28 Weeks
The best way to address this patient's concern is to perform standard gestational diabetes mellitus (GDM) screening with an oral glucose tolerance test (OGTT) at 24-28 weeks of gestation, as she does not currently have diabetes and her family history alone does not warrant earlier testing. 1
Current Clinical Status
This 21-year-old patient at 23 weeks gestation has:
- A random blood glucose of 75 mg/dL, which is normal 1
- A family history of type 2 diabetes in a relative (not specified if first-degree) 1
- No other high-risk features mentioned (normal BMI implied, no prior GDM, no prior macrosomia) 1
She does not meet criteria for early screening before 24 weeks, which is reserved for patients with specific high-risk features such as obesity, prior GDM, or previous fetal macrosomia. 1
Recommended Screening Approach
Standard Timing: 24-28 Weeks Gestation
All pregnant women should be screened for GDM at 24-28 weeks of gestation regardless of risk factors. 1 This timing is optimal because:
- Insulin resistance increases physiologically during the second and third trimesters, making GDM detectable at this point 1
- Screening earlier than 24 weeks has insufficient evidence for benefits and harms 1
- Universal screening at 24-28 weeks is the most common practice in the United States, with 96% of obstetricians routinely screening at this interval 1
Two Screening Strategy Options
Option 1: Two-Step Approach 1
- Perform a 50-g oral glucose challenge test (OGCT) in a non-fasting state
- If the result is ≥130-140 mg/dL (thresholds vary), proceed to a 3-hour 100-g OGTT
- GDM is diagnosed when 2 or more glucose values meet or exceed specified thresholds on the 3-hour test
Option 2: One-Step Approach 1
- Perform a 75-g OGTT after fasting
- Measure fasting, 1-hour, and 2-hour plasma glucose levels
- GDM is diagnosed if even 1 glucose value meets or exceeds specified thresholds
Counseling About Diabetes Risk and Fetal Effects
Reassurance Based on Current Status
You should reassure this patient that her current random glucose of 75 mg/dL is completely normal, and she does not have diabetes at this time. 1 Her family history increases her lifetime risk of type 2 diabetes but does not mean she currently has or will develop GDM during this pregnancy.
Explaining GDM Screening Rationale
GDM screening is performed to identify hyperglycemia that can increase risks of: 2, 3
- Fetal macrosomia (large baby)
- Shoulder dystocia during delivery
- Neonatal hypoglycemia
- Operative delivery and cesarean section
- Hypertensive disorders in the mother
- Neonatal respiratory distress
Treatment of GDM, when diagnosed, significantly reduces these complications and improves perinatal outcomes. 1, 2
Long-Term Considerations
If GDM is diagnosed, the patient should understand that: 1, 4, 5
- 70-85% of women with GDM can control it with lifestyle modifications alone (diet and exercise) 1
- Treatment improves immediate pregnancy outcomes 1, 2
- Women with GDM have a 50-60% lifetime risk of developing type 2 diabetes 1, 4, 5
- Postpartum screening with a 75-g OGTT at 4-12 weeks after delivery is mandatory to check for persistent diabetes 1, 4, 5
- Lifelong screening every 1-3 years is required even if postpartum testing is normal 1, 4, 5
Why Other Options Are Incorrect
A1C Now
A1C testing is not recommended for GDM screening during pregnancy. 1 While A1C can detect preexisting diabetes in early pregnancy, it is not sensitive enough for diagnosing GDM and is not part of standard screening protocols at 23 weeks. 1
Random Blood Glucose Now
Random blood glucose testing is not a valid screening method for GDM. 1 Her current random glucose of 75 mg/dL is normal but does not rule out GDM, which requires structured OGTT testing at the appropriate gestational age.
3-Hour OGTT at 24-28 Weeks
The 3-hour OGTT is a diagnostic test, not a screening test. 1 It is only performed after a positive 50-g glucose challenge test in the two-step approach. Proceeding directly to the 3-hour test without initial screening is not standard practice and subjects patients to unnecessary testing burden.
Common Pitfalls to Avoid
- Do not perform early screening (before 24 weeks) in average-risk patients based solely on family history of type 2 diabetes in a non-first-degree relative 1, 6
- Do not use A1C for routine GDM screening during pregnancy, as it lacks sensitivity for this purpose 1
- Do not skip screening even in young, healthy-appearing patients, as universal screening is recommended 1
- Do not forget to counsel about postpartum follow-up if GDM is diagnosed, as this is when many cases of persistent diabetes are detected 1, 4, 5