A cutoff of the time above the target range (TAR) of 10% or greater based on continuous glucose monitoring (CGM) in individuals being screened for gestational diabetes mellitus (GDM) was associated with 63% increased risk of adverse neonatal outcomes, according to findings of a recent study published in the American Journal of Obstetrics & Gynecology. For individuals whose TAR was less than 10%, risk was approximately 19%.
More than 1000 cases of GDM are diagnosed daily in the US, with associated adverse outcomes including hypertensive disorders of pregnancy, cesarean delivery, large for gestational age (LGA), shoulder dystocia, neonatal intensive care unit admission, hypoglycemia, and birth injuries.
In the United States, GDM is commonly diagnosed through a 1-hour glucose challenge test (GCT), followed by a 3-hour GCT if the result is abnormal, according to study authors. However, this approach has limitations in the setting of GDM and may delay treatment aimed at preventing adverse pregnancy and birth outcomes, according to study authors. They note, too, that there is inconsistency among current guidelines on GDM about the threshold of maternal hyperglycemia for a diagnosis of GDM.
The current study was designed to assess the association between CGM metrics and adverse outcome among women being screened for GDM.
Participants were recruited from a single level IV center between January 2020 and June 2022. Eligible women were aged over 18 years, received obstetrical care at 30 weeks of gestation or less, and had been screened for GDM. Exclusion criteria included known type 1 or type 2 diabetes mellitus, allergy to adhesive materials, and history of bariatric surgery.
Following a 50-g GCT, participants received and wore a blinded CGM device for 10 days. They were instructed to continue their usual dietary and lifestyle habits during monitoring. Interstitial glucose measures were obtained every 5 minutes.
Participants self measured blood glucose using a glucometer 4 times daily. A level higher than 135 mg/dL was considered abnormal. Recommended goals for GDM were fasting glucose of 95 mg/dL or less, 1-hour postprandial glucose of 150 mg/dL or less and 2-hour postprandial glucose of 120 mg/dL.
The primary outcome was a composite of adverse neonatal outcomes including LGA, respiratory distress, shoulder dystocia, need for intravenous (IV) glucose therapy, and fetal or neonatal death. Data collected included maternal demographic, antepartum, labor course, and neonatal outcomes. The Youden index was used to choose the threshold of ≥10% for TAR and association with adverse outcomes.
Of the 136 participants originally recruited, 92 were included in the final analysis; 97% completed the 1-hour GCT, with 19% having a glucose level of 135 mg/dL or more.
The overall mean 24-hour glucose was 105.4 mg/dL, and the mean within-individual coefficient of variation was 17.1%. A median 94.5% of time was spent between 63 mg/dL and 140 mg/dL, compared to a median 4.3% of time spent above 140 mg/dL. The overall mean glucose levels during the daytime and nighttime were 103.2 mg/dL and 107.5 mg/dL respectively.
The investigators reported that 17 individuals (18.5%) had time above the target range of ≥10%. These participants had a significantly higher likelihood of composite adverse neonatal outcomes than individuals with time above the target range of <10% (63% vs 18%; P=.001). In addition, when compared with neonates born to individuals with time above the target range of <10%, neonates born to individuals with time above the target range of ≥10% had an increased likelihood for hypoglycemia (14.5% vs 47%; P=.009) and had a longer length of stay (2 vs 4 days; P=.03). No difference in maternal outcomes was noted between the groups.
These results indicated increased adverse neonatal outcomes from a CGM time above target range cutoff of 10% or more in individuals receiving screening for GDM.
Investigators recommended interventional trials be conducted to determine if GDM can be diagnosed using CGM modalities and whether management based on TAR improves maternal and neonatal outcomes.
Source: Bartal MF, Cornthwaite JA, Ghafir D, et al. Continuous glucose monitoring in individuals undergoing gestational diabetes screening. Am J Obstet Gynecol. 2023;229(4):441.E1-441.E14. doi:10.1016/j.ajog.2023.04.021