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 24hr glucose profiles, and their relationship to infant birthweight 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, multicentre studies. CGM glucose metrics and 24hr glucose profiles were calculated for each gestational week and the relationship to normal (10-90th percentile) and large (>90th percentile) for gestational age (LGA) birthweight infants determined. 

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

Conclusion: Normal birthweight is associated with achieving a significantly lower mean CGM glucose concentration across the 24-hour 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 optimising maternal glycemia from early pregnancy.