(893) What’s the optimal threshold? Association of continuous glucose monitoring thresholds with adverse perinatal outcomes

Continuous glucose monitor (CGM) goals in pregnancy have been extrapolated from the American Diabetes Association (ADA) guidelines from those for nonpregnant adults (time-in-range, TIR >70%; time-above-range, TAR < 25%; time-below-range, TBR < 4%; and glycemic variability, GV ≤36%) with limited supporting data. We sought to determine risk of adverse perinatal outcomes (APOs) in people with type 1 diabetes mellitus (T1DM) using various CGM thresholds across gestation.

Study Design:

In a retrospective analysis (2019-22) of gravidas with T1DM using CGM, we determined average TAR, TIR, TBR, and GV per trimester using a target range 70-140 mg/dL. Generalized estimating equations determined odds ratios adjusted for microvascular complications (aOR) and 95% confidence intervals for hypertensive disorders of pregnancy (HDP), large-for-gestational age (LGA, birthweight ≥90%ile) and neonatal intensive care unit (NICU) admission at varying thresholds for each CGM metric in the 1^st and 3^rd trimesters.  Receiver operating characteristic analysis determined area under the curve (AUC) for each metric at each threshold.

Results: Among 92 gravidas with CGM data, HDP, LGA, and NICU admission occurred in 30 (33%), 29 (32%), and 20 (23%). For HDP, the 20% threshold for 3^rd trimester TAR and 32% threshold for 1^st trimester GV had the greatest adjusted odds (TAR: aOR 6.5, GV: aOR 7.5), and 3^rd trimester TAR < 20% had the greatest discriminatory ability (AUC 0.68, Table). For LGA, the 70% threshold for 1^st trimester TIR had the greatest adjusted odds (aOR 27.1) and discriminatory ability (AUC 0.73) of any metric. For NICU admission, the 40% threshold for 1^st trimester TAR had the greatest odds and discriminatory ability (aOR 9.1, AUC 0.74). TBR at any threshold has poor discriminatory ability (AUC ≤ 0.54) for all outcomes.

Conclusion:

In this cohort, the optimal discriminatory ability for CGM thresholds and risk of APOs in pregnancy diverge from ADA guidelines, with the exception of the 1^st trimester 70% TIR threshold for LGA risk. Larger studies should determine optimal CGM goals in pregnancy and corresponding risk of APOs.