Title: When should early screening for gestational diabetes occur?

Authors: Lorie M. Harper, MD, MSCI^1,2; Yumo Xue^1,2, Jeffrey Szychowski, PhD^1,2, Methodius Tuuli, MD, MPH³ Erika Werner, MD⁴ Jerrie Refuerzo, MD,⁵ Miriam Kupperman, PhD, MPH,⁶ Alan Tita, MD, PhD^1,2, 

Institution: 1 Center for Women’s Reproductive Health, University of Alabama at Birmingham, ²Department of Obstetrics and Gynecology, University of Alabama at Birmingham, ³Indiana University, ⁴Women and Infants of Rhode Island; ⁵The University of Texas Health Science Center at Houston; ⁶University of California, San Francisco

Background:

• Early screening for pregestational type 2 diabetes or early onset gestational diabetes is recommended by ACOG for overweight and obese women with an additional risk factor for type 2 diabetes
• Timing of early screening varies:

• • First prenatal visit
  • <14 weeks
  • <16 weeks
  • <20 weeks

• Insulin resistance increases throughout pregnancy
• Identification of gestational diabetes through glucose load testing may vary by gestational age performed due to physiologic changes in insulin resistance with advancing gestation

Objective:

Describe the impact of advancing gestational age on glucose challenge test results and the diagnosis of gestational diabetes between 14-22 weeks

Study Design:

• Secondary analysis of a multicenter randomized controlled trial of obese women with singleton non-anomalous gestations comparing early (14-20 wk) to routine (24-28 wk) screening for GDM
• Exclusion criteria: pregestational diabetes, major medical illness, bariatric surgery, or previous cesarean
• Screening was accomplished with a 50-g one hour glucose challenge test (GCT)
• Diagnostic testing with a 100-g, three-hour glucose tolerance test was performed if the GCT ≥135 mg/dL
• Gestational diabetes diagnosed with Carpenter-Coustan criteria
• Exposure was defined as the timing of early screening stratified into two week blocks: 14-15.9, 16-17.9, 18-18.9, and 20-21.9 wks
• The primary outcome was defined as the GCT value
• Secondary outcomes: Incidence of GCT≥135 mg/dL, incidence of gestational diabetes diagnosed <24 weeks, gestational age at diagnosis of GDM, composite adverse perinatal outcome (birth weight >4000 g, primary cesarean, pregnancy induced hypertension, shoulder dystocia, neonatal hyperbilirubinemia, neonatal hypoglycemia)
• Secondary analysis performed to compare the incidence of the composite adverse perinatal outcome in women undergoing routine screening (24-28 weeks) and each early screening stratum
• Baseline characteristics and outcomes were compared with a Student’s t-test, chi-squared test, or chi-squared test for trend, as appropriate

Results:

• 390 (45.5%) of 857 women underwent early screening 14-21.9 weeks
• Strata were similar in age, race, BMI, and HbA1c (Table 1)
• Women screened earlier were more likely to have hypertension (p=0.03)
• GCT value, GDM diagnosis <24 weeks, and gestational age at diagnosis of GDM did not change by timing of early screen (Table 2).
• Incidence of the primary outcome did not change by timing of early screen (Table 2)
• No timing of early screening was associated with a decrease in the primary composite outcome compared to routine screening (Figure 1)

Conclusion:

Between 14-21.9 weeks, timing of early GDM screen did not impact screening and diagnosis values, nor did it impact the effect of treatment at current screening and diagnosis thresholds.

Table 1

Table 2

Figure 1