Diabetes IV: Continuous Glucose Monitors (CGMs)
/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