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Expert commentary

by Denice Feig, MD, MSc, FRCPC

There is now good evidence that continuous glucose monitoring (CGM) is associated with improvements in maternal glucose control and neonatal health outcomes in women with type 1 diabetes, and as a consequence the use of CGM is becoming more widespread in antenatal care.

Given that lower time in range (TIR) and higher time above range during the second and third trimesters is associated with increased risk of large for gestational age infants, neonatal hypoglycemia, and neonatal intensive care unit admissions, the goal is now to increase the CGM time in range (TIR). During pregnancy, in 2019, an international consensus group recommended stricter targets for time above range, with a lower target range than for other people, of 63–140 mg/dL (3.5–7.8 mmol/L). All physicians should keep in mind that when counseling women planning pregnancy and in those who are already pregnant, greater emphasis should be placed on getting to goal as soon as possible. This study investigated differences in glycemic control and glycemic variability (GV) in 32 pregnant women with type 1 diabetes (T1D), type 2 diabetes (T2D) and gestational diabetes in the 2nd and 3rd trimesters using a Dexcom G6 CGM system worn for 10 days. While mean HbA1c was similar in the 3 groups, women with T1D spent significantly less time in the target glucose range of 63-140 mg/dl, on average 65% of the time compared to women with type 2 diabetes who spent 76% of the time in range and women with gestational diabetes who spent 92% of the time in range.  Women with T1D also spent more time above the target range compare to the other groups. Glucose variability as measured by the coefficient of variation and mean amplitude of glycemic excursions was highest in women with type 1 diabetes, intermediate in women with type 2 diabetes and lowest in women with gestational diabetes.  Thus, from this limited dataset, glycemic control and GV appeared to be better in pregnant women with T2D and gestational diabetes compared to women with T1D.

The glycemic goals of pregnancy are very tight in order to reduce excess risk for numerous maternal and fetal complications. This small study illustrates that CGM provides insights beyond A1c and highlights the need for more CGM data to identify the ideal glucose range needed to prevent maternal and fetal complications, especially in women with type 2 diabetes and gestational diabetes where less data is available. Use of continuous RT-CGM as an intervention tool during type 1 diabetes pregnancy has been shown to improve neonatal outcomes.  More research is needed to determine if the use of CGM in women with type 2 diabetes and gestational diabetes will do the same.

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