What to expect in your first month with a CGM

The first month with a continuous glucose monitor (CGM) is mostly about getting used to a new routine: putting a sensor on, keeping it on, and learning what the numbers and alerts on your phone or receiver are telling you. This guide covers the practical side. Your care team decides your targets and alert settings, and your device's user guide is the final word on how your specific system works.

Week one: the sensor and the warm-up

Every CGM has a warm-up period after a new sensor goes on, during which it shows no readings. The length depends on the system, so check your user guide and plan sensor changes for a time when a short gap is easy, such as after breakfast rather than right before bed or a drive.

Many people find the first day of a new sensor is the least consistent. If a reading looks surprising early on, that's common, and your user guide explains when to confirm with a fingerstick meter.

Why the numbers don't match your meter exactly

A CGM measures glucose in the fluid just under your skin, not in your blood. That fluid trails your blood glucose by several minutes, so when glucose is rising or falling quickly, the two numbers can look quite different. Pay attention to the trend arrow as much as the number. If how you feel doesn't match what the CGM says, follow your device's instructions and check with a meter.

A common surprise is the "compression low": lying on the sensor overnight can press on the tissue and cause a falsely low reading. If you get low alerts that disappear when you roll over, mention it to your care team and consider a different site at your next change.

Alerts: expect to adjust them

Alerts that go off too often get ignored, and alerts that never go off aren't helping. It's normal to fine-tune high and low alerts during the first few weeks. Write down which alerts felt useful and which felt like noise, and bring that list to your next appointment. Your care team should set the alert levels with you.

Keeping the sensor on

Adhesion is the most common frustration in month one. Clean the site with soap and water or an alcohol wipe, let it dry completely, and skip lotion on that spot. Use only the body sites your system is approved for. Our guide on why sensors lift early covers this in more detail.

Many people add an overpatch, a stretchy adhesive cover that goes over or around the sensor, to help it last through sweat, showers and sleep. Check your device maker's guidance first, since some say what an overpatch should and shouldn't cover.

Refills, phones and the practical bits

Set a reminder a week before you run low on sensors, since pharmacy and insurance refills can take time. If you use a phone app, check the device maker's phone compatibility list before you update your phone. Keep at least one spare sensor somewhere other than home, such as a work bag or car.

What to bring to your follow-up

Bring notes on site placement, how long each sensor lasted, any skin irritation, and which alerts you'd like to change. That's the information your care team needs to help you adjust settings. This guide can't do that for you.