Libre / A1C discrepancy during pregnancy

I’m almost 20 weeks pregnant. My 90 day Libre results indicated my average glucose is 141, or about a 6.6 A1C. Well, I just got my A1C results back, and I just had one of the best A1Cs I’ve had in a long time – it was 5.8, with an average glucose of 120! Normally I’m between 6.5 and 7.

Anyone know why there’s a discrepancy between my Libre results and my A1C blood test? I’m personally THRILLED my A1C has improved a lot during pregnancy (my most recent one had been 6.8, so it dropped a full point in the last three months!), but it’s very unusual, especially since the Libre would indicate it should be quite a bit higher.


Hi @tingbot a CGM “average” is mathematical formula, consisting of adding up individual blood sugars and dividing by the total number of readings. If your Libre estimates a1c, that too is mathematical. It would be the integration of your instantaneous blood sugar over the duration of the test time, or, if you were to draw a 3 month blood sugar versus time, it would be the exact area under the curve.

HbA1c is a chemical blood analysis estimating the average glycosylation of a quantity of blood (how much sugar is molecularly “stuck” to the blood cell). So the 3 things are different and the answers will be different.


Congrats on 20 weeks and your awesome a1c results!


@tingbot , @joe

First, congratulations.
Now to your question. The answer is as Joe has shared. The difference is in the method of determination. The sensor measures your interstitial glucose every few minutes. The total is added up & divided (plan old average). The average is compared to a table. This table gives the LIBRE A1C.

The lab A1C is a chemical analysis of % of the A1C protein.

Welcome to the world of deviations.

Hope this helps.

Thanks! I also just learned pregnancy can cause false low A1Cs because of red blood cell production differences:

My 141 average from the Libre is probably the more precise measurement, then. It falls in line with my more typical A1Cs.

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