Time-dependent gestational diabetes screening values

GYNECOLOGY & OBSTETRICS International

Journal

of Gynecology

& Obstetrics

56 (1997)

257-261

Time-dependent gestational diabetes screening values M. Getin, A. Getin* Department Received

of Obstetrics

and Gynecology,

2 July 1996; revised

Cumhuriyet

10 November

University

1996; accepted

Hospital,

Siuas, Turkey

24 November

1996

Abstract Objectiw: This study was undertaken to determine use of different cut-off values with regard to the time of the patient’s last meal in screening for gestational diabetes mellitus which could result in better results and change patient management. Methods: Two hundred and seventy-four non-diabetic women undergoing routine screening for glucose intolerance between 26 to 28 weeks’ gestation were classified with regard to the time of previous meal. A glucose challenge test and an oral glucose challenge test were conducted for each patient in the study. Results were evaluated with both a standard cut-off value of 140 mg/dl without regard to the time of the last meal and suggested cut-off values of 148 mg/dl, 142 mg/dl, and 150 mg/dl if the patient ate < 2 h, 2-3 h, and > 3 h before the screening test, respectively. Results: Two hundred and seventy-four women completed the study. With these suggested cut-off values, the number of patients with a positive glucose challenge test dropped from 15.7% to 11.3%. With these cut-off values, positive predictive value increased from 27.3% to 32.3%. Conclusions: The time since previous meal affects 50 g glucose challenge test results. These new cut-off values would lead to improved efficiency of the screening test and decreased frequency with which patients require the 3-h oral glucose tolerance test. 0 1997 International Federation of Gynecology and Obstetrics

Keywords:

Gestational

diabetes mellitus;

Glucose

challenge

test; Screening

1. Introduction

cause of the potential impact of GDM on maternal, fetal, and neonatal morbidity [21, the Second

Gestational diabetes mellitus (GDM), a carbohydrate intolerance that occurs in 3% of all pregnancies, ranges from mild degrees of hyperglycemia to insulin-dependent diabetes [l]. Be-

and Third International Workshop Conferences on Gestational Diabetes and The American Diabetes Association have recommended universal screening for GDM [31. The suggested strategy is that pregnant women undergo a 50 g l-h glucose challenge test (GCT) between 24 and 28 weeks gestation, with a cut-off value of 140 mg/dl and without regard to the time or the nature of the

*Corresponding Fakultesi, Kadin 0020-7292/97/%17.00 PZZ SOO20-7292(96)

author, Cumhuriyet Universitesi H. ve Dogum ABD, 58140 Sivas, Turkey. 0 1997 International 02831-7

Federation

Tip

of Gynecology

and Obstetrics

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M. Getin, A. Getin /International

Federation

previous meal [4]. Patients with l-h plasma glucose values 2 140 mg/dl undergo a 100 g 3-h oral glucose tolerance test (G’IT). Although the 50 g l-h GCT has been used to detect GDM since 1959 and has a 79% sensitivity and 87% specificity, several studies have questioned whether the accepted cut-off value of 140 mg/dl should be changed based on use of the fasting or fed condition before the 50 g l-h GCT and noted that the use of different cut-off values seems warranted [5-71. This study was designed to evaluate the suggested cut-off values of the Toronto Tri-Hospital Gestational Diabetes Project [7] for screening GDM. 2. Patients and methods

This prospective study was conducted from October 1994 to January 1996 at the Cumhuriyet University Hospital, Sivas, Turkey. Of the obstetric population of 344 women, 291 women aged 2 24 years and with 24 to 28 weeks’ gestation were eligible for enrolment in the study, provided that there was no history of preexisting diabetes or regular ingestion of any drug, and that they were examined by an obstetrician before 20 gestational weeks. The following were excluded from the study: preexisting diabetes, multiple pregnancy, preterm premature rupture of membranes, preeclampsia, and delivery I 28 weeks’ gestation. Consenting eligible patients screened for GDM from 24 to 28 weeks’ gestation with a 50 g, l-h GCT, completed without dietary directions during morning hours. To assure consistency in testing procedures, all women were instructed to return 1 week later and a 100 g oral GTT was performed in the morning after an overnight fast of 8-12 h after 3 days of a 150 g carbohydrate diet and unrestricted physical activity. The glucose oxidase method was used for plasma blood glucose determination. For evaluation of data according to the Toronto Tri-Hospital Gestational Diabetes Project results [7], these women were grouped according to the time interval between the last meal and 50 g GCT administration:

of Gynecology

and Obstehics

56 (1997) 257-261

Group A: the GCT was performed at < 2 h since the previous meal and considered positive in patients whose results reported as more than a standard cut-off of 140 mg/dl and a suggested cut-off of 148 mg/dl. Group B: the GCT was performed at 2-3 h since the previous meal. Screening test was considered positive if plasma glucose is more than both a standard cut-off of 140 mg/dl and a suggested cut-off of 142 mg/dl. Group C: the GCT was performed at > 3 h since the previous meal and considered positive if plasma glucose is more than both a standard cut-off of 140 mg/dl and a suggested cut-off of 150 mg/dl. The diagnosis of GDM was established in the presence of two or more of the following values on the oral GTE fasting 2 105 mg/dl, l-h 2 190 mg/dl, 2-h 2 165 mg/dl, and 3-h 2 145 mg/dl. Patients with only one abnormal value were subjected to repeat testing 1 week later. After abnormal glucose intolerance was demonstrated with an oral GIT, those women whose fasting and 2-h postprandial plasma glucose remained < 105 mg/dl and 120 mg/dl, respectively, with a prescribed diabetic diet were defined as class A, gestational diabetic patients. Antenatal testing was started at 34 weeks for all the patients. Gestational age was confirmed by reliable menstrual dates and early prenatal care or ultrasonography at < 21 weeks. Pre-pregnancy body mass index (BMI) was calculated as the body weight (kg) divided by the square of the height cm’). For analysis, obesity was defined as a BMI over 25 kg/m2. Macrosomia was considered to be predicted if (1) an ultrasonographic estimate of fetal weight exceeded the 90th percentile for gestational age and (2) an ultrasonographic estimate of fetal weight was 2 4000 g on admission to labor and delivery. Plasma glucose values were given to the attending physician and patient only if gestational diabetes was diagnosed by oral GCT. Clinical and perinatal characteristics of patients were collected from the study groups. Prevalence of GDM

M. Getin, A. Getin /International

Federation

was calculated for all of the patients. Diagnostic indices sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of GCT evaluated with standard and suggested cut-off values were calculated for three study groups and all the patients. Comparisons between proportions were performed with ,y2 test and presented as percentages. Data with normal distribution were analyzed with one-way analysis of variance test and data without normal distribution were analyzed with Kruskal-Wallis one-way analysis of variance test where appropriate. Differences were considered statistically significant if P < 0.05. Data are presented as mean + S.D., median (range), proportion as appropriate.

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3. Results

Two hundred and ninety-one patients were recruited for the study. Seventeen patients were excluded: among those were 6 preexisting diabetes, 3 multiple pregnancy, 3 preterm premature rupture of membranes, 3 preeclampsia, and 2 delivery I 28 weeks’ gestation. Two hundred and seventy-four patients (123 in Group A, 95 in Group B, and 56 in Group C) completed the study. The prevalence of GDM in this population was 6.2%. During the study period, 17 Class A, gestational diabetic patients (8 in Group A, 5 in Group B, and 4 in Group C) were identified with

Table 1 Clinical characteristics of patients in groups A, B, and C Characteristics Age (Years> Gravihity (No.) Parity (No.) Pre-pregnancy weight (kg) BMI (kg/m*) Obesity (No.) Maternal weight gain (kg) Family history of diabetes mellitus (No 1.1 History of Gestational diabetes mellitus (No.) Macrosomia (No.) Stillbirth Preeclampsia (No.)

Group A

Group B = 95)

(n

Group C (n = 56)

Significance

(n = 123)

27 (19-37) 2 (l-7) 1 (O-5) 64 (42-100) 24.8 (17.3-40.1) 41 (33.3%) 5 (4-7) 6 (4.9%)

28 (18-37) 2 (l-7) 1 (O-5) 63 (42-100) 24.5 (17-40) 39 (41.1%) 5 (4-8) 7 (7.4%)

29 (19-41) 2 (l-8) 1 (O-6) 63.5 (47-102) 25 (19.3-39.8) 18 (32.1%) 5 (4-7) 5 (8.9%)

0.566 0.838 0.934 0.615 0.598 0.408 0.173 0.554

3 (2.4%) 9 (7.3%) 4 (3.3%) 4 (3.3%)

1 (1.1%) 8 (8.4%) 2 (2.1%) 4 (4.2%)

2 (3.6%) 5 (8.9%) 1 (1.8%) 3 (5.4%)

0.575 0.921 0.798 0.796

Table 2 Comparison of perinatal characteristics of the study subjects Characteristics Gestational age at delivery (weeks) Birth weight (g) Cesarean section Macrosomia Polyhydramnios Apgar score < 7 at 1 min Apgar score < 7 at 5 min Admission to neonatal unit

Group A (n = 67)

Group B (n = 37)

Group C

39 (38-41) 3473.5 & 390.5 20 (16.3%) 13 (10.6%) 7 (5.7%) 6 (4.9%) 2 (1.6%) 2 (1.6%)

39 (38-41) 3394.7 f 416.5 14 (14.7%) 8 (8.4%) 5 (5.3%) 4 (4.2%) 1 (1.1%) 0

39 (38-41) 3407.2 + 425.6 6 (10.7%) 5 (8.9%) 3 (5.4%) 3 (5.4%) 1 (1.8%) 0

Significance

(n = 25)

0.933 0.321 0.621 0.855 0.990 0.949 0.916

260

M. Getin, A. Getin /International

Federation

oral GTT. Table 1 presents the clinical characteristics of the subjects. The groups are comparable in the characteristics considered. Table 2 shows the comparison of perinatal characteristics among the three groups.There were no significant differences in all the perinatal characteristics among the three groups. Two patients in Group A were admitted to the neonatal unit for about 4 days. There were no maternal and perinatal deaths and no serious maternal and perinatal morbidity. According to results of the oral GTT, the results of the GCT with standard and suggested cut-off values in the study groups and all the patients are presented in Table 3. Because of the small sample size, statistical comparisons of the standard and suggested cut-offs of the three groups and all patients could not be performed. There were less positive results with new cut-off values during oral GCT (15.7% vs. 11.3%). Of 12 patients whose screening test values exceeded 140 mg/dl, one had GDM (8.3%), which was higher than the 6.2% in the general population. In Group A, there is a decrease in sensitivity (75% vs. 62.5%), increases in specificity (86% vs. 91.3%) and in PPV (27.3% vs. 33.3%), and a decrease in NPV (98% vs. 97.2%). In Group B, there is no change in sensitivity, an increase in specificity (88.9% vs. 92.2%), and no changes in PPV and NPV. In Group C, there are no changes in sensitivity, increases in specificity (88.5% vs. 92.3%) and in PPV (25% vs. 33.3%), and a decrease in Table 3 Comparison

of standard

and suggested Group

True (+) False (+) False ( - ) True (-) Sensitivity Specificity Positive predictive Negative predictive Prevalence

value value

cut-off

values

A (n = 123)

of glucose Group

of Gynecology

and Obstetrics

56 (1997)

257-261

NPV (97.9% vs. 95.9%). In all the patients, there is a decrease in sensitivity (64.7% vs. 58.8%), increases in specificity (87.5% vs. 91.8%) and in PPV (27.3% vs. 32.3%), and no change in NPV. 4. Discussion

Undiagnosed GDM is known to increase perinatal morbidity and mortality, this increase has been associated with many factors, such as congenital malformations, asphyxia, macrosomia, birth trauma, and neonatal hypoglycemia [8]. In spite of two decades of study, the best method of screening GDM and the choice of optimum cut-off values for the GCT remain controversial [1,5,9-111. The use of lower cut-off values may identify more women with lesser degrees of glucose intolerance, but the benefits of this approach may not be uniform because factors other than specific plasma glucose values may increase perinatal morbidity observed in women with GDM. Some studies also suggest that increasing carbohydrate intolerance among patients not meeting the current criteria for the diagnosis of GDM leads to increased rates of unfavorable maternal and perinatal outcomes [3,12-141. Kitzmiller et al. [31 have reported that patients with abnormal GCT results but normal oral GTT results are at increased risk, as are those with one abnormal oral GTI value rather than the two required by the National Diabetes Data Group criteria. To study whether a difference is present in the

challenge

test among

B (n = 95)

Group

the study groups All patients

(n = 274)

Standard cut-off (140 mg/dl)

Suggested cut-off (148 mg/dl)

Standard cut-off (140 mg/dl)

Suggested cut-off (142 mg/dl)

Standard cut-off (140 mg/dl)

C (n = 56) Suggested cut-off (150 mg/dl)

Standard cut-off (140 mg/dl)

Suggested cut-offs

6 16 2 99 7.5 86 27.3 98 6.2

5 10 3 105 62.5 91.3 33.3 97.2 6.2

3 10 2 80 60 88.9 30 97.6 6.2

3 7 2 83 60 92.2 30 97.6 6.2

2 6 2 46 50 88.5 25 97.9 6.2

2 4 2 48 50 92.3 33.3 95.9 6.2

11 32 6 225 64.7 87.5 27.3 97.1 6.2

10 21 7 236 58.8 91.8 32.3 97.1 6.2

.

M. Getin, A. Getin /International

Federation

three study groups, we examined the various factors in mothers from all three groups and the analysis of clinical and perinatal variables showed no differences among three groups. The results of this study indicate that there was a decrease (4.4%) in positivity of GCT with new suggested cut-off values in all three groups. With these suggested cut-off values, the overall false-positive rate was decreased by 4% and the overall falsenegative rate was increased by 0.3%. With the adoption of suggested cut-off values during GCI, sensitivity decreased by 5.9%, specificity increased by 4.3%, and positive predictive value increased by 5% in all three groups. In 12 patients with whom screening test values exceeded 140 mg/dl but below the suggested cut-offs, prevalence of GDM is higher than in the general population (8.3% vs. 6.2%). We thought this high proportion resulted from small sample size (l/12 vs. 17/274) and these data were insufficient to be adequately evaluated. This study demonstrates that the time since the previous meal affects the result of GCT when pregnant women are screened for glucose intolerance between the 24th to 28th week of pregnancy. Sermer et al. [7] suggested that GCT cut-off values of 148 mg/dl, 142 mg/dl, and 150 mg/dl should be used if patients ate < 2 h, 2-3 h, and > 3 h before the GCT, respectively. Our study also demonstrates that the adoption of these new cut-off values improves efficiency of the GCT, and decreases the number of patients who should go on to the definitive oral GTT. Approximately 4.4% reduction of indirect and direct health care costs may be possible in our hospital. References [l]

Schwartz JG, Phillips WT, Blumhardt MR, Langer 0. Use of a more physiologic oral glucose solution during screening for gestational diabetes mellitus. Am J Obstet Gynecol 1994; 171: 685.

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