Accuracy of continuous glucose monitoring during exercise in type 1 diabetes pregnancy

Kavita Kumareswaran, Daniela Elleri, Janet M Allen, Karen Caldwell, Marianna Nodale, Malgorzata E Wilinska, Stephanie A Amiel, Roman Hovorka, Helen R Murphy

Research output: Contribution to journalArticlepeer-review

30 Citations (Scopus)


BACKGROUND: Performance of continuous glucose monitors (CGMs) may be lower when glucose levels are changing rapidly, such as occurs during physical activity. Our aim was to evaluate accuracy of a current-generation CGM during moderate-intensity exercise in type 1 diabetes (T1D) pregnancy. 

SUBJECTS AND METHODS: As part of a study of 24-h closed-loop insulin delivery in 12 women with T1D (disease duration, 17.6 years; glycosylated hemoglobin, 6.4%) during pregnancy (gestation, 21 weeks), we evaluated the Freestyle Navigator(®) sensor (Abbott Diabetes Care, Alameda, CA) during afternoon (15:00-18:00 h) and morning (09:30-12:30 h) exercise (55 min of brisk walking on a treadmill followed by a 2-h recovery), compared with sedentary conditions (18:00-09:00 h). Plasma (reference) glucose, measured at regular 15-30-min intervals with the YSI Ltd. (Fleet, United Kingdom) model YSI 2300 analyzer, was used to assess CGM performance. 

RESULTS: Sensor accuracy, as indicated by the larger relative absolute difference (RAD) between paired sensor and reference glucose values, was lower during exercise compared with rest (median RAD, 11.8% vs. 18.4%; P<0.001). These differences remained significant when correcting for plasma glucose relative rate of change (P<0.001). Analysis by glucose range showed lower accuracy during hypoglycemia for both sedentary (median RAD, 24.4%) and exercise (median RAD, 32.1%) conditions. Using Clarke error grid analysis, 96% of CGM values were clinically safe under resting conditions compared with only 87% during exercise. 

CONCLUSIONS: Compared with sedentary conditions, accuracy of the Freestyle Navigator CGM was lower during moderate-intensity exercise in pregnant women with T1D. This difference was particularly marked in hypoglycemia and could not be solely explained by the glucose rate of change associated with physical activity. 

Original languageEnglish
Pages (from-to)223-229
Number of pages7
JournalDiabetes Technology & Therapeutics
Issue number3
Early online date27 Feb 2013
Publication statusPublished - 12 Mar 2013


  • Adult
  • Blood Glucose
  • Blood Glucose Self-Monitoring
  • Type 1 Diabetes Mellitus
  • Exercise Test
  • Female
  • Great Britain
  • Glycosylated Hemoglobin A
  • Humans
  • Hypoglycemic Agents
  • Insulin
  • Insulin Infusion Systems
  • Ambulatory Monitoring
  • Motor Activity
  • Pregnancy
  • Pregnancy in Diabetics
  • Reproducibility of Results
  • Sedentary Lifestyle

Cite this