Screening for diabetes in pregnant and postpartum patients

GTT: glucose tolerance test; ADA: American Diabetes Association; ACOG: American College of Obstetricians and Gynecologists; BMI: body mass index; A1C: glycated hemoglobin; GCT: glucose challenge test; USPSTF: United States Preventive Services Task Force.

* ADA and ACOG define patients at increased risk of overt diabetes based on:

• BMI ≥25 kg/m² (≥23 kg/m² in Asian Americans) plus one or more of the following:
  • Gestational diabetes mellitus in a previous pregnancy
  • A1C ≥5.7% (39 mmol/mol), impaired glucose tolerance, or impaired fasting glucose on previous testing
  • First-degree relative with diabetes
  • High-risk race/ethnicity (eg, African American, Latino, Native American, Asian American, Pacific Islander)
  • History of cardiovascular disease
  • Hypertension (≥140/90 mmHg) or on therapy for hypertension
  • High-density lipoprotein cholesterol level <35 mg/dL (0.90 mmol/L) and/or a triglyceride level >250 mg/dL (2.82 mmol/L)
  • Polycystic ovary syndrome
  • Physical inactivity
  • Other clinical condition associated with insulin resistance (eg, severe obesity, acanthosis nigricans)
  • Previous birth of an infant weighing ≥4000 grams

UpToDate includes older age as a risk factor for early testing and uses age 40 years as the threshold.

¶ There is no consensus on the type of test to administer. Options include any of the following:

• One-step test (eg, 2-hour, 75 gram oral GTT)
• Two-step test (1-hour, 50 gram GCT without regard to time of day/previous meals; screen-positive patients go on to have a 3-hour 100 gram oral GTT)
• A1C only; a diagnosis of overt diabetes is made when A1C is ≥6.5% (≥48 mmol/mol)

Refer to the UpToDate topic on screening and diagnosis of diabetes mellitus in pregnancy for detailed information on types of tests and interpretation.

Δ Both ADA and ACOG suggest early pregnancy testing for undiagnosed type 2 diabetes in patients with risk factors. Some clinicians screen all patients by obtaining an A1C with the routine prenatal laboratory tests. By contrast, a USPSTF guideline concluded available evidence was insufficient to assess the balance of benefits and harms of screening asymptomatic pregnant patients for glucose intolerance before 24 weeks of gestation.

◊ Either a one-step or two-step diabetes screening test can be used.

§ Postpartum, a fasting plasma glucose test is a reasonable alternative to the GTT but does not allow for diagnosis of impaired glucose tolerance; A1C can also be substituted in patients in whom obtaining a fasting specimen is especially inconvenient, but it performs less well in postpartum patients because of increased peripartum red cell turnover. For subsequent testing, refer to the UpToDate topic on screening and diagnosis of diabetes mellitus in pregnancy.