Grand Rounds

Can Immediate Glucose Tolerance Testing Postpartum Predict Results of 6-12 week GTT?

BACKGROUND AND PURPOSE:

ACOG recommends 6- to 12-week glucose tolerance test (GTT) postpartum for women with GDM to identify impaired glucose metabolism or overt diabetes
The American Diabetes Association (ADA) moved the timing up to a 4- to 12-week postpartum window to test more women prior to 6-week postpartum visit
Compliance with current guidelines remains poor (approximately 50%)
Dinglas et al. (Amer J Perinatol, 2017) sought to assess if immediate GTT is predictive of the 6-12 week follow-up GTT

Prospective cohort study (2013-2016)
‘2 step’ criteria were used for GDM screening (see ‘Related ObG Topics’ below)
Subjects participated in a 75 g, 2-hour GTT on postpartum days 2 through 4 and instructed to follow up in 6- to 12-weeks for postpartum glucose testing
- ADA guidelines used to diagnose prediabetes and overt diabetes (see ‘Related ObG Topics’ below)
Sensitivity, specificity, PPV, and NPV of the immediate GTT were used to predict abnormal 6- to 12-week postpartum
Due to limited enrollment, considered a ‘pilot study’

197 participants approached, 87 women consented and 80 completed immediate testing
35 women underwent both immediate GTT and a 6- to 12-week postpartum glucose testing
- Sensitivity: 100%
- Specificity: 42.8%
- PPV: 30.4%
- NPV: 100%
Immediate HbA1c
- Significantly correlated with immediate GTT
- Not significantly correlated with 6- to 12-week GTT

Present study confirmed poor adherence with 6-12 week GTT recommendations similar to previous literature (55%)
High NPV and sensitivity is similar to previous research
A negative immediate GTT could reduce the need for the 6- to 12-week GTT in approximately 30% of women with GDM
A positive immediate GTT may identify women who require closer follow-up
Based on the positive pilot, study recruitment and collaboration are now ongoing

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