Continuous glucose monitoring metrics and birthweight: informing management of type 1 diabetes throughout pregnancy

OBJECTIVE: To determine gestational weekly changes in continuous glucose monitoring (CGM) metrics and 24-h glucose profiles and their relationship to infant birth weight in pregnant women with type 1 diabetes.

RESEARCH DESIGN AND METHODS: An analysis of >10.5 million CGM glucose measures from 386 pregnant women with type 1 diabetes from two international multicenter studies was performed. CGM glucose metrics and 24-h glucose profiles were calculated for each gestational week, and the relationship to normal (10–90th percentile) and large (>90th percentile) for gestational age (LGA) birth weight infants was determined.

RESULTS: Mean CGM glucose concentration fell and percentage of time spent in the pregnancy target range of 3.5–7.8 mmol/L (63–140 mg/dL) increased in the first 10 weeks of pregnancy and plateaued until 28 weeks of gestation, before further improvement in mean glucose and percentage of time in range until delivery. Maternal CGM glucose metrics diverged at 10 weeks of gestation, with significantly lower mean CGM glucose concentration (7.1 mmol/L; 95% CI 7.05–7.15 [127.8 mg/dL; 95% CI 126.9–128.7] vs. 7.5 mmol/L; 95% CI 7.45–7.55 [135 mg/dL; 95% CI 134.1–135.9]) and higher percentage of time in range (55%; 95% CI 54–56 vs. 50%; 95% CI 49–51) in women who had normal versus LGA. The 24-h glucose profiles were significantly higher across the day from 10 weeks of gestation in LGA.

CONCLUSIONS: Normal birth weight is associated with achieving significantly lower mean CGM glucose concentration across the 24-h day and higher CGM time in range from before the end of the first trimester, emphasizing the need for a shift in clinical management, with increased focus on using weekly CGM glucose targets for optimizing maternal glycemia from early pregnancy.