CGM reveals nighttime hyperglycemia in gestational diabetes
A cohort of women with gestational diabetes received more comprehensive information on nocturnal hyperglycemia with use of a continuous glucose monitor than through self-monitoring blood glucose, according to study data.
“Masked CGM data revealed nocturnal hyperglycemia in those who were not commenced on insulin, with 60% of subjects breaching glucose targets overnight for [greater than] 10% of time,” David N. O’Neal, MD, FRACP, a clinical endocrinologist in the department of medicine at St. Vincent’s Hospital, University of Melbourne, and colleagues wrote in a study published in Diabetes Technology & Therapeutics. “The SMBG measurement following the evening meal usually occurred between 7 p.m. and 10 p.m., and this blood glucose measurement at a single time-point would have provided only a limited insight into overnight hyperglycemia, as would the prebreakfast reading.”
Researchers conducted an observational cohort study of women with gestational diabetes who were between 24 and 28 weeks of gestation at the Werribee Mercy Hospital and Mercy Hospital for Women in Melbourne, Australia. Participants received dietary and lifestyle advice and were taught SMBG at an education session within 2 weeks of gestational diabetes diagnosis. On the same day as the education session, participants began using a Medtronic iPro CGM device for a 7-day period. CGM data were masked to treating providers and participants. Insulin was not immediately initiated in the week CGM data were collected.
All participants were instructed to record diet and SMBG levels at least four times per day during the CGM week. They were asked to eat three meals and three snacks per day, avoid carbohydrates, and walk 10 to 15 minutes after each meal. Insulin was prescribed if the self-monitoring target of less than 100 mg/dL fasting glucose or less than 120 mg/dL 2-hour post-meal glucose was breached three times in the week.
Researchers enrolled 90 women in the study from December 2017 to March 2019 (mean age, 32 years); 34 were prescribed insulin and 56 managed their gestational diabetes with only diet and lifestyle adjustments. BMI, fasting oral glucose tolerance tests, SMBG and CGM all showed the insulin cohort spent more time in hyperglycemia than those who did not receive insulin (P = .0001)
Researchers analyzed the amount of time spent in hyperglycemia for participants who managed their diabetes without insulin. In this cohort, 61% went above their CGM glycemic target for more than 10% of the time between midnight and 6 a.m. From 6 a.m. to midnight, 20% went above their target. Most hyperglycemia occurred between midnight and 3 a.m., and 47% of participants who spent less than 10% of time in hyperglycemia during the day had hyperglycemia for 10% or more time at night.
By contrast, SMBG results showed only 5.4% of participants who did not use insulin exceeded their post-dinner target of 120 mg/dL. In measurements taken in the morning before breakfast, none of the women exceeded their fasting glucose target of 100 mg/dL.
Researchers said CGM provides individuals with a more detailed look at the magnitude and duration of glucose fluctuations. The data could be used in clinical decision-making for women with gestational diabetes.
“We have proposed a set of CGM cutoffs based on previous studies, with goals set differently for nighttime and daytime ranges,” the researchers wrote. “Further studies are required to determine the incidence of large for gestation babies and other pregnancy-related outcomes in a larger cohort of gestational diabetes patients, which would help better define the correct CGM targets. Once these cutoffs have been established, interventions aimed at targeting these nocturnal glucose levels will need to be formally tested against outcomes.”