October 6, 2012

CGM, Pregnancy, A1C and What are the Right Questions.

Just read this short write up of a CGM and pregnancy study: http://www.obgynnews.com/news/top-news/single-article/continuous-glucose-monitoring-offers-no-pregnancy-benefit/5699b76dcc1c8cbf0d16e9d4160a94bc.html I'll call the study Secher after the good doctor who did the study. 

It seems to me Secher et al studied intermittent use of a CGM because they thought getting full time compliance would be hard. They found that intermittent, what they more or less defined as non compliant, use was not a benefit. Another earlier study by Murphy, et al found the opposite: http://www.bmj.com/highwire/filestream/384096/field_highwire_article_pdf/0/bmj.a1680

I would love to see more detail but it seems the Secher study may be asking the wrong asking the question. It asks does partial CGM help not does CGM help. Is this normal research? - to only look at intermittent use that the designs see as a surrogate of non compliant use? What happen with more compliant use and dose that use lead to less total glycemic variability.

A statement in the article attributed to Secure's says, "By focusing on severe hypoglycemia, we might pay a price in hyperglycemic complications. " This seems to indicate that they were not focused on balanced control of BG but more hypo avoidance. The study is not reported out yet so one can not  know for sure. If so then, the complication of hyperglycemia were not addressed as highs weren't the focus. This seems to be the case as a write up of the study states that s secondary outcome of this study was, "Metabolic control in terms of HbA1c, blood sugar measurements and the occurrence of severe hypoglycemia in pregnant diabetic patients." (http://clinicaltrials.gov/ct2/show/NCT00994357) To me, and I am no expert, that suggests they were focused on lows not highs. However it is the highs, in the third trimester, that may be the issue.

The Murphy paper says, "Prepregnancy care is key to improved glycaemic control during the first two trimesters but does not reduce the risk of macrosomia, which we believe is more strongly associated with hyperglycemia in later gestation.12 Data from the Netherlands suggest that near optimal glycaemic control during early pregnancy (84% of women had a mean HbA1c level of 7.0% or less) failed to reduce the risk of macrosomia, present in 48.8% infants.1 This prompted us to consider new strategies, focusing on reducing postprandial hyperglycaemic spikes during the second and third trimesters. Observational data suggest a strong correlation between maternal postprandial glucose levels in the third trimester with an increased risk of macrosomia.13-17 Educational approaches incorporating additional glucose testing after meals to improve glycaemic control in late gestation have shown potential to reduce birth weight.18 19 " So it seems to me the issue isn't the device but how the moms to be are coached and supported to learn and manage BG with the CDM device. Still this second paper reports out A1Cs.

I would love to see these studies talk about variability, maybe measured as standard deviation, particularly in the third trimester, in addition to A1C. CGM is a tool to report and so facilitate management to minimize variability in ways finger stick can not. I would love a study that looks at the question - can women be coached and supported to manage glycemic variability with a CGM in ways that reduce third term hypers and hypos that has an impact on birth weights? Is this variability management more predictive of healthy birth weight than A1C? 

That seems to me to be closer to the right questions or is it just me?

ps. It was really hard for me not to make jokes here. Sadly I would think that if Secher is used to deny CGM insurance coverage as an option to help coach women in pregnancy it would be a case of Murphy's law not Murphy's study. 

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