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  Continuous Glucose Monitoring for the Evaluation ofGravid Women With Type 1 Diabetes Mellitus  Yariv Yogev,  MD , Rony Chen,  MD , Avi Ben-Haroush,  MD , Moshe Phillip,  MD ,Lois Jovanovic,  MD , and Moshe Hod,  MD OBJECTIVE: Tocomparethedailyglycemicprofilereflectedbycontinuous and intermittent blood glucose monitoring inpregnant women with type 1 diabetes and to compare thetreatment protocols based on the two monitoring methods. METHODS: The study sample consisted of 34 gravid patientsat gestational weeks 16–32, with type 1 diabetes being treated by multiple insulin injections. Data derived fromthe continuous glucose monitoring system for 72 hours were compared with fingerstick glucose measurementsperformed 6–8 times per day. During the study period,patients documented the time of food intake, insulin injec-tions, and hypoglycemic events. Data on demographics,gravidity, parity, body mass index, hemoglobin A1c, andfructosamine levels were collected for each patient. RESULTS:  An average (  standard deviation) of 780  54glucose measurements was recorded for each patient withcontinuous glucose monitoring. The mean total time of hyperglycemia (glucose level greater than 140 mg/dL) un-detected by the fingerstick method was 192  28 minutesper day. Nocturnal hypoglycemic events (glucose level lessthan 50 mg/dL) were recorded in 26 patients; in all cases,there was an interval of 1–4 hours before clinical manifes-tations appeared or the event was revealed by randomblood glucose examination. Based on the additional infor-mation obtained by continuous monitoring, the insulintherapeutic regimen was adjusted in 24 patients (70%). CONCLUSION:  Continuous glucose monitoring can diagnosehigh postprandial blood glucose levels and nocturnal hy-poglycemic events that are unrecognized by intermittent blood glucose monitoring and may serve as a basis for determining treatment regimens. A large, prospectivestudy on maternal and neonatal outcome is needed toevaluate the clinical implications of this new monitoring technique. (Obstet Gynecol 2003;101:633–8. © 2003 byThe American College of Obstetricians and Gynecolo-gists.)  Thegoalofmanagementintype1diabetesistomaintain blood glucose and hemoglobin (Hb)A1c levels as near tonormal as possible. This goal is difficult to achieve in all patients and poses an even greater challenge in pregnantwomen.Improved glycemic control during diabetic pregnancyhas been found to decrease perinatal morbidity andmortality, 1,2 aswellasthecongenitalmalformationrate. 3 On the one hand, however, too-tight glycemic control inthis patient group may be accompanied by a high inci-denceofhypoglycemia,rangingfrom36%to71%. 4,5 Onthe other hand, as maternal glycemia increases, the riskof macrosomia, the most common and significant peri-natal complication clearly associated with diabetes in pregnancy, increases as well. 6 Patients with diabetic pregnancy are treated with multiple insulin injectionsand are advised to perform self–blood glucose monitor-ing by fingerstick measurements 4–8 times per day. Theoptimal frequency of blood glucose testing in gravid patients with type 1 diabetes has not been established. The self–blood glucose monitoring method has animportant limitation; it provides only a single valueduring the day and does not allow for continuous, lon-gitudinal monitoring. As such, it may be missing bothhypoglycemic and hyperglycemic events. To counterthis problem, a new technology of continuous glucosemonitoring was recently developed (Mastortotoro J,Levy R, Georges LP, White N, Mestman J. Clinicalresults from a continuous glucose sensor multi-centerstudy [abstract]. Diabetes 1998;47:A61). The systemmeasures interstitial glucose levels in subcutaneous tis-sue, within a range of 40–400 mg/dL. Glucose valuesobtained with continuous glucose monitoring have beenshown to correlate with laboratory measurements of  plasma glucose levels 7 and with home glucose metervalues (Mastortotoro J, et al. Diabetes 1998;47:A61). The purpose of the present study was to compare thedaily glycemic profile reflected by continuous and inter-mittent blood glucose monitoring in pregnant womenwithtype1diabetesandtodeterminewhethertreatment From the Perinatal Division and The World Health Organization Collaborating Center, Department of Obstetrics and Gynecology, Rabin Medical Center, Beilinson Campus, and Institute for Endocrinology and Diabetes, National Center of  Childhood Diabetes, Schneider Children’s Medical Center of Israel, Petah Tiqva,Israel; Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel; and Sansum Medical Research Institute, Santa Barbara, California. 633 VOL. 101, NO. 4, APRIL 2003 0029-7844/03/$30.00© 2003 by The American College of Obstetricians and Gynecologists. Published by Elsevier. doi:10.1016/S0029-7844(02)02714-X  strategy protocols based on the two monitoring methodsdiffer. MATERIALS AND METHODS  The initial study sample consisted of 41 consecutivegravid women with type 1 diabetes who were recruitedforthisprospectivestudyduringaroutineclinicalvisittothe Diabetes in Pregnancy Center of the Perinatal Divi-sion Unit, Rabin Medical Center between November2001andMarch2002.Ofthese,34women(82.9%)gaveconsent to participate after receiving a comprehensiveexplanation of the study. The local ethics committeeapproved the study protocol.Inallcases,type1diabetesmellituswasdiagnosedbeforethe onset of the current pregnancy. Gestational age rangedfrom 16 to 32 weeks. All patients were being treated withinsulin and were under the care of a registered dietitian forindividualized counseling and instructions. At entry to the study, the patient’s chart was reviewedfor demographic data, gravidity, parity, and body massindex(BMI).Priortosensorplacement,levelsofHbA1c,fructosamine, and plasma glucose were measured. The MiniMed continuous glucose monitoring system(MiniMed, Sylmar, CA) was used in all cases for 3 days. The system measures glucose levels in subcutaneousinterstitial tissue. It is composed of a disposable subcuta-neous glucose-sensing device and an electrode impreg-nated with glucose oxidase connected by a cable to alightweight monitor, which is worn over the clothing oronabelt.Thesystemtakesaglucosemeasurementevery10 seconds, based on the electrochemical detection of glucose by its reaction with glucose oxidase, and storesan average value every 5 minutes, for a total of 288measurements each day. A communication device en-ables the data stored in the monitor to be downloadedand reviewed on a personal computer. The patients areunaware of the results of the sensor measurements dur-ing the monitoring period. The same trained nurse placed all continuous glucosemonitoringsensors.Priortoplacement,thesiteontheflankwas prepared with an alcohol sponge, and the sensor wascalibrated according to the manufacturer’s instructions. Thepatientswereshownhowtocodethetimeoffoodintake, insulin injections, exercise periods, and symp-tomatic hypoglycemic events into the monitor.Patients were instructed to wear the continuous glu-cosemonitoringdevicefor72consecutivehours.During this period, they also performed fingerstick capillaryglucose measurements in the morning after overnightfastingand2hoursaftermeals(6–8timesperday)using a glucometer (Ames Glucometer Elite, Bayer Corp.,Elkhart, IN) and self-coded the data into the monitor. Atthe end of the study period, before the nurse discon-nected the women from the sensor, plasma and glucom-eterglucosevaluesweremeasured.Qualitycontrolmea-sures of glucose levels from the meter, sensor, and plasma glucose were also performed at the time of con-nection to the continuous glucose monitoring systemand again at study completion. The data collected byself–blood glucose monitoring and continuous glucosemonitoringforeachpatientwereevaluatedseparatelybya single experienced physician. The average time (inminutes) per day of sensor glucose readings of less than50 mg/dL and greater than 140 mg/dL was calculatedfrom the daily graphs. A hypoglycemic event was de-fined as a greater than 30-minute asymptomatic reading  below 50 mg/dL or symptomatic hypoglycemia detected by meter or monitoring records. The decision regarding the insulin regimen was madetwice, first on the basis of the self–blood glucose moni-toring data and then on the basis of the continuousglucose monitoring data. To prevent bias, the two typesof data were presented to the physician on differentoccasions. The physician was blinded to the identity of the individual patients.Continuous parameters are given as means    stan-dard deviations. Pearson correlation coefficient ( r  ) andthe significance for it ( P  ) were calculated between thevariables. Reliability coefficient was used to quantitatethe consistency of the two measuring methods (self– blood glucose monitoring and continuous glucose mon-itoring) applied to each subject. Paired  t   test was used todetermine the statistical significance of differences inmean continuous parameters. A  P   value equal to or lessthan .05 was considered statistically significant. RESULTS Mean patient age was 26    4.7 years (range 21–36years), and mean gestational age was 25    6.2 weeks(range 16–32 weeks). Mean gravidity and parity were2.4    1.1 and 1.2    0.9, respectively. Mean BMI was26.2  4.7 kg/m 2 , mean HbA1c level 6.1  1.2% (nor-mal range 4.5–5.7%), and mean fructosamine level 276  29 mg/dL (normal range 205–285 mg/dL). Allpatientscompletedthe3-daystudy.Therewerenoadverse events associated with the use of continuousglucose monitoring. None of the patients experiencedirritation or infection at the insertion site. Although patientswereblindedtothecontinuousglucosemonitor-ing readings during the study period, they reported highsatisfaction using the device concerning potential future benefits of continual monitoring. An average of 780    54 glucose measurements wasrecorded for each patient with continuous glucose mon- 634 Yogev et al  Glucose Monitoring, Gravidas, and Type 1 DM  OBSTETRICS & GYNECOLOGY  itoring. The mean total time of hyperglycemia (glucoselevel greater than 140 mg/dL) undetected by the finger-stick method was 192  28 minutes per day. Nocturnalhypoglycemic events (glucose level less than 50 mg/dL)were recorded in 26 patients; in all cases, there was aninterval of 1–4 hours before clinical manifestations ap- peared or the event was revealed by random bloodglucose examination. Mean glucose level by self–bloodglucose monitoring and continuous glucose monitoring was 101  13 mg/dL and 121  13 mg/dL, respectively( P     .02). The individual glucose levels varied widelyduring each 24-hour period, but the overall 3-day profileof each patient remained consistent in many occasionsduring this time period (Figure 1). Analysis of the whole study group for the total 102days of continuous monitoring showed that all 34 pa-tients had undetected hyperglycemia by self–blood glu-cosemonitoring,witharangeof74–303minutesperday(mean 192  28 minutes per day, median 166 minutes).Nocturnal hypoglycemic events (at bedtime, during the night, and in the early morning) were recorded in 26of the 34 patients in 58 nights; symptoms occurred in 28episodes in 17 patients. In all affected patients, there wasan interval of 1–4 hours before clinical manifestationsappeared or the event was revealed by random bloodglucose examination. There was no statistically significant correlation be-tween HbA1c and fructosamine levels and the occur-rence of hypoglycemic events.Figure 2 demonstrates a 24-hour continuous record-ing in one of the patients.In 24 of the 34 patients (70%), the physician recom-mendedthattheinsulinregimenformulatedonthebasisof the self–blood glucose monitoring data be changed onsubsequent evaluation of the continuous glucose monitor-ing data. The most common change made was in decreas-ing the long or intermediate-acting insulin dosage at night(mean reduction by 25% in the nighttime dose of insulin). The correlation coefficient ( r  ) between the glucose mea-surements by the sensor and meter was .93    .04, and betweentheplasmaglucose,metermonitoring,andsensorrecording, .91  .02. The reliability coefficient was .88. DISCUSSION Despite years of meticulous study, there is still a paucityof information regarding the optimal level of glycemia indiabetic pregnancy that clinicians should target to safely Figure 1.  Three-day continuous glucose monitoring profile in one of our patients, showing significant variations in glucoselevels during the day but a similar daily glycemic profile for all 3 days. Yogev. Glucose Monitoring, Gravidas, and Type 1 DM. Obstet Gynecol 2003. 635 VOL. 101, NO. 4, APRIL 2003  Yogev et al  Glucose Monitoring, Gravidas, and Type 1 DM  reduce maternal and perinatal morbidity. Strict meta- bolic control in patients with type 1 diabetes has beenassociated with an increased risk of maternal hypoglyce-mia. In our study, continuous monitoring of blood glu-cose in women with diabetic pregnancies confirmed thehigh occurrence rate of nocturnal hy poglycemia sus- pected in earlier studies. Rosenn et al 5 reported signifi-cant hypoglycemia, defined as hypoglycemia requiring assistancefromanotherperson,in71%ofgravidpatientswith type 1 diabetes, with a peak incidence in the firsttrimester. The impact of maternal hypoglycemia on hu-man fetal development and neonatal outcome has not been extensively studied. Although concern about thehazards of hypoglycemia is related primarily to the preg-nantmother,thepotentialeffectsonthedevelopingfetusneed to be considered as well.Studies in rat and mice embryos point to a possiblefetal risk of malformations in the presence of short- andlong-term maternal hypoglycemia. 8  These findings were not apparent with self–bloodglucose monitoring. Indeed, Data derived from continu-ous glucose monitoring led the evaluating physician tochange the insulin regimen, usually by decreasing thenighttime dose of intermediate-acting insulin. In morethan half the cases, the hypoglycemic events were sub-clinical, diagnosed only by continuous glucose monitor-ing, and in one fifth of the patients, more than onehypoglycemic event occurred during the night. These findings may indicate that continuous glucosemonitoring is a better monitoring method than self– blood glucose monitoring in detecting hypoglycemicevents, which are usually asymptomatic and occur atnight. Whereas stringent glycemic control may lead tohypoglycemia, too-loose control poses a risk of macroso-mia, the most common and significant perinatal compli-cation associated with diabetic pregnancy, which canlead to an increased risk of birth injuries and asphyxia. The risk of macrosomia rises as maternal glycemia in-creases. In addition, intensified management of gesta-tional diabetes reduces the rate of perinatal complica-tions, normalizes birth weight, 9 and has a positiveinfluence on the congenital malformation rate. 3 Our study showed that glucose levels were above theupper normal threshold for many hours during the day. These events were related to unscheduled meals and between-meal snacks and were not detected by conven-tional self–blood glucose monitoring protocols. Despitethe recent introduction of intensified treatment proto- Figure 2.  A 24-hour continuous glucose monitoring trace in one of our patients demonstrating a nocturnal hypoglycemiaevent, with a latent phase of 1 hour before clinical symptoms appeared (marked by the patient and followed by a meal).Note the undetectable hyperglycemia by the self – blood glucose monitoring method after the meal in early morning. Yogev. Glucose Monitoring, Gravidas, and Type 1 DM. Obstet Gynecol 2003. 636 Yogev et al  Glucose Monitoring, Gravidas, and Type 1 DM  OBSTETRICS & GYNECOLOGY

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Jul 23, 2017
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