Diabetes IV: Continuous Glucose Monitors (CGMs)

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Background 

  • What is a continuous glucose monitor? 

    • CGM - a wearable device typically put on the back of the arm, stomach, or buttocks that is composed of a sensor and a transmitter 

      • The sensor is a small needle/probe that sits in the skin and measures interstitial blood sugar 

      • It typically will clip into a transmitter that can then send this information to a device (ie. via bluetooth to your phone or to a website that your physician can check) 

      • Sometimes, it requires scanning the transmitter with a phone or another device to show the blood sugar 

    • Some logistics 

      • Typically can be worn for 7-14 days 

      • Should be active >70% of the time 

    • Other cool things it can do 

      • Also, certain CGMs can sync with insulin pumps to help better regulate blood sugar (ie. closed-loop insulin technology) 

  • Who will you see that has a CGM? 

    • Most likely patients with T1DM - insurance is more likely to cover 

    • Some patients with T2DM, though much less common 

    • Now, it seems that more patients with GDM who are not able to do fingersticks may obtain or desire a CGM.

    • Glycemic targets in pregnancy

      • Remember that the ADA and ACOG recommends targets for fasting of <95 mg/dL, 1 hr postprandial <140 mg/dL, and 2-hour postprandial of <120 mg/dL  

What are the numbers I should be looking at in a CGM? 

  • The targets can be confusing because instead of just 4 time points, we now have many, many more! 

    • Many CGMs will sample blood sugar every 5 minutes 

  • Things to look at should be glucose targets 

    • Targets can be individualized, but in pregnancy, the target should be between 63-140 mg/dL per the ADA 

    • Can ask patient to generate a report for you or when you log into their reports, you can generate a report for the last XX amount of days 

    • Some people will spend some time both above and below target (note that some patients’ targets may be individualized and different) 


Is a CGM actually useful in treating diabetes? (ie. does it improve outcomes?) 

    • Multiple studies done in patients with T1DM and pregnancy 

  • Largest: Continuous Glucose Monitoring in Women with Type 1 Diabetes in Pregnancy (CONCEPTT) - multicenter RCT that compared self-monitored blood glucose + CGM to SMBG alone in 325 women who were either planning pregnancy or who were pregnancy 

    • Those with CGM had a small but statistically significant difference in A1C (-0.19%) 

    • Those with CGM in pregnancy had statistically significant less time above range than control, without an increase in time below range or in number of severe hypoglycemic episodes 

    • Also there were differences in neonatal outcomes! 

      • In CGM group, there was lower incidence of:

        • LGA

        • Neonatal hypoglycemia,

        • NICU admissions

  • What about T2DM? 

    • Outcomes here are less robust, and there are fewer studies - no RCTs have specifically studied T2DM in pregnancy with CGM to date 

  • GDM?

    • Largest study was prospective cohort in 2014 - 340 women with GDM who had 4 weeks of blinded CGM + standard care or standard care alone

      • Those blinded to CGM had lower rate of preeclampsia, improvement in CGM metrics, and lower rate of neonatal composite outcome (ie. premature delivery, macrosomia, LGA status, SGA, obstetric trauma, neonatal hypoglycemia, hyperbilirubinemia, and respiratory distress)  

    • Studies also show that those with CGM are more likely to receive insulin therapy 

  • So some conclusions: 

    • Clearly, CGM can improve outcomes in T1DM and those that are pregnant

    • Less clear in those who have T2DM and GDM 

How do I manage those with CGMs? 

  • This should be done with endocrinology or MFM 

    • The goal is to get the patient at least 70% into the target range as described above

    • We won’t go into pumps  

  • For those with injectable insulin

    • It is still helpful to look at when the patient is having spikes in blood sugar and adjust based off of that 

  • If there are spikes after breakfast or dinner → add fast acting or regular insulin at those times 

  • If there are spikes with lunch → can either add fast acting with lunch or increase long acting in the morning 

  • If there are spikes with fasting, look at overnight glucose 

    • If there is a drop in glucose in the middle of the night (ie. 4 am) and then an increase, this is known as the Somogyi effect 

    • The way to address this is either (1) to decrease night time long acting insulin or (2) to add a protein snack after dinner 

  • If overall blood sugar is elevated in the AM between meals, can increase AM long acting insulin