Gestational Diabetes: Why does the same food give very different results?

A bowl of Cheerios (3/4 c. - the kids under 12 serving size) with a cup of 1% milk send my blood glucose to 138 one day and 159 another day?!

I'm allowed 30 grams of carbs for breakfast. This breakfast was less than 30. It's not the total carbs, because I've had breakfasts with closer to 30 carbs successfully. My breakfasts yesterday -- a mini bagel with peanut butter -- had more total carbs but the same amount of protein.

I can't figure this out. It's frustrating!

My fasting level was 81 before my Cheerios breakfast today. It was 5 points less, 76, two days ago when I had the same breakfast.

My mini bagel with peanut butter breakfast was a whole wheat mini bagel with natural peanut butter (peanuts and salt are the only ingredients). My fasting level before this breakfast was 77. After breakfast it was 128.

Regarding exercise, I went for a long walk (more than a mile/more than 40 minutes) yesterday after dinner. I didn't exercise at all the day before my first (and "better") Cheerios breakfast.

My highest self-test in two weeks of doing this has been 163 after one hour (I've been told to aim for 140 or less after one hour.)

First of all, it's not that different. Home testing meters are allowed by the FDA to have a 10% error rate. So you might only be seeing a couple point difference.

Another issue would be what your blood sugar started out at before you ate. Was it exactly the same on all days? If not, it's not a controlled experiment.

Also, blood sugar is affected by many things, not just food. Most important is exercise. The amount of exercise you got in the previous 24 hours can affect your readings.

Another thing is Tylenol. It can cause an artificially high reading.

The breakfast with the peanut butter had more fat in it than the cereal breakfast. That may help slow down/even out the sugar rise.

Many people are especially resistant in the morning, when other hormone levels are high. If your readings at other times, and your fasting reading are all OK, then I would say you are doing OK. If all your postprandials are this high, you may need to go back to your provider to adjust your diet.

EDIT: Ok, I read your additional details. Listen, blood sugar is a moving target and you're only taking a snapshot. It sounds like you're working at it and trying hard and that's all you can do.

Another big factor that I forgot to mention earlier is stress. Stress releases cortisol which blocks insulin and causes high blood sugar. Both good stress and bad stress do this. Anything you can do to avoid stress or reduce it will be helpful.

If most of your blood sugars are in your target range, than you're doing great.

The worst that can happen is you will end up on insulin. This is not the worst thing in the world, and is very safe for your baby.

As long as you are sticking to your diet plan and logging your data as instructed, then you are doing your job. If a lot of your tests are above the target range, then call your provider and talk to him/her about making changes. That's really all you can do because it's not an exact science due to the many factors at play.

Keep up the good work!