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CME Credit Offered
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Poster Session 2

(404) Circadian Variations of Glucose Challenge Test Results In Pregnancy: Examining Non-Linear Trends

Thursday, January 30, 2025
4:00 PM – 6:00 PM  
Objective: Research has documented circadian variations in glucose challenge test (GCT) results by comparing morning to afternoon collection. Variations by collection time have implications for the performance of potentially unnecessary glucose tolerance tests (GTTs). However, more detailed examination of the complex non-linear trends in GCT results across collection times has yet to be conducted.  Therefore, we aim to examine non-linear relations between collection time and GCT values using polynomial regression.

Study Design:

This is a retrospective cohort study of all pregnancies 2017-2023 for which GCT was collected after 24 weeks in a community hospital in New York. Patients with pregestational diabetes mellitus (DM), or early diagnosis of DM in the 1st or 2nd trimester were excluded. To examine non-linear trends in GCT values, we used polynomial regression with a stepwise approach to adding polynomial terms to the initial linear model, assessing model fit with each inclusion. 

Results:

Our sample included 5341 pregnancies for which GCT was collected. The sample was highly racially/ethnically diverse (Asian: 23.62%, Hispanic/Latino: 66.39%, Other: 10.99%). In the final model, we found significant linear (B=.47, p=.034), quadratic (B= -.18, p < .001), and cubic terms (B= -.02, p < .001), indicating a non-linear relationship of GCT values with collection time. Evaluation of inflection points showed that GCT values reached a local maximum at approximately 1:30pm. 

Conclusion:

GCT values vary with diurnal rhythms, such that observed values appear to increase throughout the AM, peak in the early afternoon, and then trend downwards. These findings have clinical implications, as GCTs collected in the afternoon may lead to more false positives and potentially unnecessary further testing by GTT.  Overall, these data suggest that GDM screening protocols that include the GCT should be refined to account for the effect of time of day on test performance.