Clinical Review

How to improve outcomes in gestational diabetes— for mother and baby

OBG Manag. 2011 March;23(3):36-45

References

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9. De Luca AK, Nakazawa CY, Azevedo BC, Rudge MV, De Araujo Costa RA, Calderon IM. Influence of glycemic control on fetal lung maturity in gestations affected by diabetes or mild hyperglycemia. Acta Obstet Gynecol Scand. 2009;88(9):1036-1040.

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For more on the use of oral agents in GDM, see Dr. Aaron B. Caughey’s commentary on the subject of this issue.

Continuous monitoring may detect occult hyperglycemia and hypoglycemia

The traditional method of monitoring the blood glucose level is to stick a finger to obtain a blood sample and use a test strip and a meter to measure the concentration of glucose in the sample. Most meters on the market are reasonably accurate. However, research has demonstrated that they are least accurate during episodes of hypoglycemia.²⁷

Automated continuous glucose-monitoring systems are less intrusive than the traditional method, but they are usually reserved for people who have type 1 diabetes requiring intensive insulin therapy. However, because data suggest that even short periods of hyperglycemia or hypoglycemia can be detrimental to a developing fetus, there is increasing interest in utilizing continuous glucose monitoring for GDM.

Several research groups have compared continuous glucose monitoring with finger-stick monitoring and found that women randomized to continuous monitoring have lower mean hemoglobin A_1c levels from 32 to 36 weeks’ gestation.^28,29 (See “Exploring the value of continuous glucose monitoring in gestational diabetes?”) Women undergoing continuous monitoring also have:

lower mean birth-weight standard- deviation scores
lower median customized birth-weight centiles
a reduced risk of macrosomia.

One study found that information gleaned from continuous glucose monitoring provided additional information that altered clinical management in 42 of 68 (62%) cases. These additional data included evidence of undetected and potentially dangerous postprandial hyperglycemia and overnight hypoglycemia.²⁹

Yogev and colleagues found that continuous glucose monitoring is significantly more sensitive than traditional methods in detecting periods of hypoglycemia in women who have GDM. They also found that asymptomatic hypoglycemic events are common during pharmacotherapy in gestations affected by GDM.³⁰ The same group used continuous glucose monitoring at night in obese, nondiabetic women to identify previously undetected:

high postprandial glucose peak values
increased 1- and 2-hour postprandial glucose levels
increased time to the glucose peak
significantly lower mean blood glucose levels.³¹

Insurers were reluctant to cover continuous glucose monitoring devices when they first became available. Since then, however, much progress has been made. Nevertheless, inadequate reimbursement for the time it takes a clinician to change a patient’s treatment regimen and her subsequent management remains a significant barrier to adoption of these systems.³² The key to success with continuous glucose monitoring is to train the patient to use it properly.

INTEGRATING EVIDENCE AND EXPERIENCE

Exploring the value of continuous glucose monitoring in gestational diabetes

Tanenberg R, Bode B, Lane W, et al. Use of the Continuous Glucose Monitoring System to guide therapy in patients with insulin-treated diabetes: a randomized controlled trial. Mayo Clin Proc. 2004;79(12):1521–1526.

Hypoglycemia is the most common adverse event among patients undergoing intensive insulin therapy. as a result, many insulin users keep their hemoglobin A_1c level above recommended thresholds to protect against hypoglycemia.

The American Diabetes association recommends that patients on insulin self-monitor blood glucose three or four times daily to guide adjustments in therapy and ensure a stable and optimal hemoglobin A_1c level. “however, adherence to frequent blood-glucose monitoring is low, and less than 54% of patients with insulin-treated diabetes are reported to self-monitor their blood glucose at least three times each day,” say tanenberg and coworkers.

To determine whether use of a continuous glucose-monitoring system improves metabolic control, the investigators randomized 109 patients who had insulin-treated diabetes to continuous monitoring or frequent self-monitoring. at enrollment, all patients had insulin-treated diabetes and inadequate metabolic control. at the end of the study, both groups used continuous monitoring for 3 days; these values were used to calculate measures of hypoglycemia.

In the study, the women in the self-monitoring group were counseled to measure capillary blood glucose a minimum of four times daily, as well as when they experienced symptoms of hypoglycemia, which was defined as a blood glucose measurement of 60 mg/dL or lower. any hypoglycemic event was considered to be over when the measurement exceeded 60 mg/dL for at least 30 minutes.

Findings

Hemoglobin A_1c levels were similar between groups at baseline, and both groups showed significant (P < .001) and similar (P=.95) improvement in these levels after 12 weeks of study. however, the continuous-monitoring group had a significantly shorter duration of hypoglycemic events than the self-monitoring group at week 12 (49.4±40.8 minutes vs 81.0±61.1 minutes per event, respectively; P=.009).

Tanenberg and coworkers hypothesize that the improvement in hemoglobin A_1c in the self-monitoring group was a result of monitoring that was more frequent (7 times a day) than is typical. they concluded that use of continuous monitoring to guide therapy adjustments in patients who use insulin significantly reduces the duration of hypoglycemia, compared with adjustments guided by self-monitoring values alone.