Research Article Volume 6 Issue 1
Department of Obstetrics and Gynecology, Alexandria University, Shatby Maternity hospital, Egypt
Correspondence: Eman Ali Abd El Fattah, Department of Obstetrics and Gynecology, Faculty of Medicine, Alexandria University, Shatby Maternity hospital, 4, fathia Baheeg St, Fleming, Alexandria, Egypt
Received: February 11, 2017  Published: October 27, 2017
Citation: Fattah EAAEI. Diagnostic ability of the fetal ultrasonographic parameters in screening for gestational diabetes. MOJ Womens Health. 2017;6(1):344356. DOI: 10.15406/mojwh.2017.06.00148
Pancreatic βcell hyperplasia occurring in normal pregnancy results in higher fasting and postprandial insulin levels. In addition, placental hormones cause increased insulin resistance, especially throughout the third trimester. Pregnancies with GDM are associated with increased obstetric complications. Therefore, the surveillance of GDM during pregnancy is especially important. The best method for screening continues to be controversial. O' Sullivan, is the most widely used screening test and is recommended by the ADA. GDM of any severity increases the risk of fetal macrosomia which can be diagnosed by ultrasonography Increased body weight is due to organomegaly and increased fat deposition. Increased glucose transfer from the diabetic mother to the fetus and placenta results in fetal hyperglycemia and hyperinsulinemia, promoting growth of insulindependent tissues and organs, such as the liver. The aim of the present study is to test the efficiency of ultrasound parameters (biparietal diameter, abdominal circumference, estimated fetal weight, fetal truncal subcutaneous fat layer, and fetal liver length) against the efficiency of the 50gram oral glucose challenge test (O’ Sullivan test) to screen for gestational diabetes in the second trimester between 2428weeks of gestation.
The study enrolled three hundred second trimester pregnant subjects selected from outpatient clinic coming for antenatal visit at 2428weeks gestation. All recruited patients were subjected to history taking, complete clinical examination, ultrasound examination(Including: fetal biometry measurements to confirm gestational age, detailed anomaly scan, fetal subcutaneous fat layer, length of the right lobe of the liver, abdominal circumference, biparietal diameter, head circumference, femur length, and estimated fetal weight calculated by (Hadlock AC,BPD) in grams O'Sullivan test was done, patients were considered screen positive if plasma venous glucose concentration ≥140md/dl or 7.8mmol/L. 100 gram oral glucose tolerance curve was used to confirm or rule out the diagnosis of gestational diabetes. A blood glucose level below 180 mg after one hour was considered normal. A blood glucose level below 140 mg after two hours is considered normal. Two or more abnormally high readings are considered Diabetes.
Gestational diabetes mellitus (GDM) is a condition of glucose intolerance with onset in pregnancy 1,2) It is associated with increased obstetric complications, such as fetal macrosomia, neonatal hypoglycemia and hypocalcemia, as well as maternal hypertension and thromboembolic disease. Therefore, surveillance for GDM is important.^{1,2} Women at risk should be tested at the first antenatal visit using the American Diabetes Association diagnostic criteria for non pregnant adults.^{2} The 50g nonfasting 1h glucose challenge test (GCT) is the most widely implemented screen used. Alternative screening methods have been proposed to increase the detection rates of GDM and to overcome these shortcomings of the GCT. Some are based on ultrasound examinations. Although uncomplicated GDM with less severe fasting hyperglycemia has not been associated with increased perinatal mortality, GDM of any severity increases the risk of fetal macrosomia.^{3} Increased glucose transfer from the diabetic mother to the fetus and placenta results in fetal hyperglycemia and hyperinsulinemia, promoting growth of insulindependent tissues and organs, such as the liver.^{4} The aim of the present study is to test the efficiency of ultrasound parameters (biparietal diameter, abdominal circumference, estimated fetal weight, fetal truncal subcutaneous fat layer, and fetal liver length) against the efficiency of the 50 gram oral glucose challenge test (O’ Sullivan test) to screen for gestational diabetes in the second trimester between 2428 weeks of gestation.
The study enrolled three hundred second trimester pregnant subjects selected from outpatient clinic coming for antenatal visit at 2428 weeks gestation, with or without history of gestational diabetes in a previous pregnancy. Subjects with pregestational diabetes were excluded. Consent was taken from all subjects to participate in the study. All recruited patients were subjected to history taking, complete clinical examination, ultrasound examination(Including: fetal biometry measurements to confirm gestational age, detailed anomaly scan, fetal subcutaneous fat layer, length of the right lobe of the liver, abdominal circumference, biparietal diameter, head circumference, femur length, and estimated fetal weight calculated by (Hadlock AC,BPD) in grams. All examinations were performed by the same sonologist (E.A) using an HDI 1500 scanner equipped with a 3.5MHz transducer (Medison ultrasound, SonoR7). To measure the fetal anterior abdominal wall fat, the abdominal circumference was selected. The measurement was taken as close to vertical as possible. The quadrant that included the spine was avoided. The measurements were taken from the inner to the outer aspect of the echogenic subcutaneous fat that surrounded the abdomen. Patient is considered screen positive if expected fetal weight or abdominal circumference is above the 90th percentile for age, or measured fat layer equals to or exceeds 3.5mm at 2428 weeks gestation. To measure liver length, the tip of the right lobe was clearly identified and the liver length was measured from the dome of the right hemidiaphragm to the tip of the right lobe (Figure 1). O'Sullivan test was done; patients received 50 gram glucose orally irrespective of their fasting state. Blood sugar level was evaluated one hour later. Patients were considered screen positive if plasma venous glucose concentration ≥ 140 md/dl or 7.8 mmol/L.^{5} Screen positive cases were subjected to 100 gram oral glucose tolerance curve: (2 hours 100 gram OGTT) to confirm or rule out the diagnosis of gestational diabetes. The patient's blood glucose was recorded at baseline after eight hours fasting. The patient was then given 100 gram glucose orally then blood glucose was measured at one hour and two hours. The diagnosis of GDM was based on the criteria of the World Health Organization, which is considered the gold standard. A blood glucose level below 180 mg after one hour was considered normal. A blood glucose level below 140 mg after two hours is considered normal. One abnormal reading denotes glucose intolerance and requires further assessment at a later gestation (later than 28 weeks). Otherwise; abnormal reading on two occasions of the 100 gram OGTT, the patient is diagnosed as having gestational diabetes.
Statistical methodology
Data were collected and entered to the computer using SPSS (Statistical Package for Social Science) program for statistical analysis (ver 21).^{5} Data were entered as numerical or categorical, as appropriate. When KolmogorovSmirnov test revealed no significance in the distribution of variables, parametric statistics was carried out, while in the notnormally distributed data the nonparametric statistics was carried out.^{6}
An alpha level was set to 5% with a significance level of 95%, and a beta error accepted up to 20% with a power of study of 80%. In Table 1 & Figure 2, gestational age was statistically not significant (p>0.05). On the other hand a statistically significant difference was found in results of OGTT between cases with positive O' Sullivan test and cases with negative O' Sullivan test (p=0.000) (Table 2) & (Figure 3), fetal abdominal circumference (p=0.001) (Table 3) & (Figure 4), fetal Biparietal diameter (p=0.000) (Table 4) & (Figure 5), Femur length (p=0.000) (Table 5 and Figure 6), expected fetal weight (p=0.000) (Table 6) & Figure 7), Abdominal subcutaneous tissue fat (p=0.000) (Table 713) & (Figure 8). No statistically significant difference found between cases with positive OGTT and cases with negative OGTT as regards Fetal liver length as p=0.060 (Table 8) & (Figure 916).
OGTT Negative (n=293) 
OGTT Positive (n=7) 
All Cases (n=300) 

Minimum 
22 
23 
22 
Maximum 
34.86 
26 
34.86 
Mean 
23.94 
24.76 
23.96 
Std. Deviation 
1.338 
1.0192 
1.336 
Median 
23.857 
25 
23.857 
Interquartile range 
22.85725.000 
23.85725.428 
22.85725.00 
KS test of normality 
D=0.073 
D=0.198 
D=0.071 
p=0.001* 
p=0.200 NS 
p=0.001* 

MannWhitney U Test 
Z=1.862, p=0.063 NS 
Table 1 Gestational age
OGTT Negative(n=293) 
OGTT Positive(n=7) 
All Cases(n=300) 

Minimum 
62 
95 
62 
Maximum 
203 
212 
212 
Mean 
90.15 
181 
92.27 
Std. Deviation 
19.892 
39.319 
24.62 
Median 
87 
190 
88 
Interquartile range 
77.0096.00 
183.00204.00 
78.0096.00 
KS test of normality 
D=0.152 
D=0.377 
D=0.193 
p=0.000* 
p=0.003* 
p=0.000* 

MannWhitney U Test 
Z=4.124, p=0.000* 
Table 2 O’Sullivan test (mg/dl)
OGTT Negative(n=293) 
OGTT Positive(n=7) 
All Cases(n=300) 

Minimum 
17.55 
20.21 
17.55 
Maximum 
23.41 
23.55 
23.55 
Mean 
19.4757 
21.74 
19.5285 
Std. Deviation 
1.17601 
1.3696 
1.22699 
Median 
19.18 
21.78 
19.19 
Interquartile range 
18.4620.61 
20.2523.31 
18.4920.71 
KS test of normality 
D=0.115 
D=0.164 
D=0.117 
p=0.000* 
p=0.200 NS 
p=0.000* 

MannWhitney U Test 
Z=3.421, p=0.001* 
Table 3 Abdominal circumference (cm)
OGTT Negative(n=293) 
OGTT Positive(n=7) 
All cases(n=300) 

Minimum 
4.39 
6.08 
4.39 
Maximum 
7.07 
7.04 
7.07 
Mean 
5.8455 
6.6386 
5.864 
Std. Deviation 
0.37773 
0.3812 
0.39577 
Median 
5.84 
6.8 
5.855 
Interquartile range 
5.5606.125 
6.2507.030 
5.56256.1500 
KS test of normality 
D=0.057 
D=0.235 
D=0.060 
p=0.022* 
p=0.200 NS 
p=0.010* 

MannWhitney U Test 
Z=3.860, p=0.000* 
Table 4 Biparietal diameter (cm)
OGTT Negative(n=293) 
OGTT Positive(n=7) 
All Cases(n=300) 

Minimum 
2.83 
4.48 
2.83 
Maximum 
7.39 
5.14 
7.39 
Mean 
4.2494 
4.8186 
4.2627 
Std. Deviation 
0.42555 
0.26959 
0.43095 
Median 
4.2 
4.9 
4.22 
Interquartile range 
3.954.50 
4.525.10 
3.95254.5175 
KS test of normality 
D=0.093 
D=0.190 
D=0.091 
p=0.000* 
p=0.200 NS 
p=0.000* 

MannWhitney U Test 
Z=3.635, p=0.000* 
Table 5 Femur length (cm)
OGTT Negative(n=293) 
OGTT Positive(n=7) 
All cases(n=300) 

Minimum 
395 
717 
395 
Maximum 
1172 
1144 
1172 
Mean 
661.2321 
938.8571 
667.71 
Std. Deviation 
118.74135 
171.47247 
126.97159 
Median 
625 
978 
631.5 
Interquartile range 
568.00751.00 
755.001130.00 
568.25759.00 
KS test of normality 
D=0.122 
D=0.162 
D=0.122 
p=0.000* 
p=0.200 NS 
p=0.000* 

MannWhitney U Test 
Z=3.640 

p=0.000* 
Table 6 Expected fetal weight (gram)
OGTT Negative(n=293) 
OGTT Positive(n=7) 
All cases(n=300) 

Minimum 
1.8 
3.9 
1.8 
Maximum 
4.7 
4.9 
4.9 
Mean 
3.0567 
4.3 
3.0857 
Std. Deviation 
0.56314 
0.35119 
0.58951 
Median 
3 
4.2 
3.05 
Interquartile range 
2.603.50 
4.004.50 
2.603.50 
KS test of normality 
D=0.084 
D=0.184 
D=0.073 
p=0.000* 
p=0.200 NS 
p=0.001* 

MannWhitney U Test 
Z=4.373, p=0.000* 
Table 7 Abdominal subcutaneous tissue fat (cm)
OGTT Negative(n=293) 
OGTT Positive(n=7) 
All Cases(n=300) 

Minimum 
30 
30 
30 
Maximum 
38 
37 
38 
Mean 
31.78 
33.71 
31.83 
Std. Deviation 
1.655 
2.752 
1.706 
Median 
31 
34 
31.5 
Interquartile range 
30.0032.50 
30.0036.00 
30.0033.00 
KS test of normality 
D=0.199 
D=0.256 
D=0.200 
p=0.000* 
p=0.185 NS 
p=0.000* 

MannWhitney U Test 
Z=1.883 

p=0.060 NS 
Table 8 Fetal liver length (mm)
ROC curve
Variable 
Abdominal Circumference (cm) 
Classification Variable 
OGTT_Diagnosis 
Sample size 
300 
Positive group: OGTT Diagnosis = 1 
7 
Negative group: OGTT Diagnosis = 0 
293 
Disease prevalence (%) 
2.33 
Area under the ROC curve (AUC)
Area under the ROC curve (AUC) 
0.878 
Standard Error^{a} 
0.0615 
95% Confidence Interval^{b} 
0.836 to 0.913 
z statistic 
6.148 
Significance level P (Area=0.5) 
<0.0001 
^{a}DeLong et al.^{8}
^{b}Binomial exact
Youden Index
Youden index J 
0.6587 
95% Confidence Interval^{a} 
0.5714 to 0.7143 
Associated criterion 
>20.2 
95% Confidence Interval^{a} 
>20.12 to >21.69 
Sensitivity 
100 
Specificity 
65.87 
Table 9 Abdominal circumference (cm)
^{a}BC_{a}bootstrap confidence interval (1000 iterations; random number seed: 978)
ROC curve
Variable 
Biparietal diameter (cm) 
Classification Variable 
OGTT Diagnosis 
Sample Size 
300 
Positive group: OGTT Diagnosis = 1 
7 
Negative group: OGTT Diagnosis = 0 
293 
Disease prevalence (%) 
2.33 
Area under the ROC curve (AUC)
Area under the ROC curve (AUC) 
0.927 
Standard Error^{a} 
0.0431 
95% Confidence Interval^{b} 
0.891 to 0.954 
z statistic 
9.894 
Significance level P (Area=0.5) 
<0.0001 
^{a}DeLong et al.^{8}
^{b}Binomial exact
Youden Index
Youden index J 
0.7036 
95% Confidence Interval^{a} 
0.6314 to 0.8055 
Associated criterion 
>6.24 
95% Confidence Interval^{a} 
>6.07 to >6.74 
Sensitivity 
85.71 
Specificity 
84.64 
Table 10 Biparietal diameter (cm)
^{a}BC_{a}bootstrap confidence interval (1000 iterations; random number seed: 978)
ROC Curve
Variable 
Femur Length (cm) 
Classification variable 
OGTT Diagnosis 
Sample size 
300 
Positive group: OGTT Diagnosis = 1 
7 
Negative group: OGTT Diagnosis = 0 
293 
Disease prevalence (%) 
2.33 
Area under the ROC curve (AUC)
Area under the ROC curve (AUC) 
0.902 
Standard Error^{a} 
0.0457 
95% Confidence Interval^{b} 
0.863 to 0.933 
z statistic 
8.795 
Significance level P (Area=0.5) 
<0.0001 
^{a}DeLong et al.^{8}
^{b}Binomial exact
Youden Index
Youden Index J 
0.7235 
95% Confidence Interval^{a} 
0.6485 to 0.7816 
Associated Criterion 
>4.46 
95% Confidence Interval^{a} 
>4.42 to >4.51 
Sensitivity 
100 
Specificity 
72.35 
Table 11 Femur length
^{a}BC_{a}bootstrap confidence interval (1000 iterations; random number seed: 978)
ROC Curve
Variable 
Expected fetal weight (gram) 
Classification Variable 
OGTT Diagnosis 
Sample size 
300 
Positive group: OGTT Diagnosis = 1 
7 
Negative group: OGTT Diagnosis = 0 
293 
Disease Prevalence (%) 
2.33 
Area under the ROC curve (AUC)
Area under the ROC curve (AUC) 
0.902 
Standard Error^{a} 
0.0511 
95% Confidence Interval^{b} 
0.863 to 0.934 
z statistic 
7.876 
Significance level P (Area=0.5) 
<0.0001 
^{a}DeLong et al.^{8}
^{b}Binomial exact
Youden Index
Youden Index J 
0.6758 
95% Confidence Interval^{a} 
0.5904 to 0.7411 
Associated Criterion 
>712 
95% Confidence Interval^{a} 
>708 to >829 
Sensitivity 
100 
Specificity 
67.58 
Table 12 Expected fetal weight (gram)
^{a}BC_{a}bootstrap confidence interval (1000 iterations; random number seed: 978)
ROC Curve
Variable 
Abdominal subcutaneous tissue fat (cm) 
Classification variable 
OGTT Diagnosis 
Sample size 
300 
Positive group: OGTT Diagnosis = 1 
7 
Negative group: OGTT Diagnosis = 0 
293 
Disease prevalence (%) 
2.33 
Area under the ROC curve (AUC)
Area under the ROC curve (AUC) 
0.983 
Standard Error^{a} 
0.00819 
95% Confidence Interval^{b} 
0.961 to 0.994 
z statistic 
58.952 
Significance level P (Area=0.5) 
<0.0001 
^{a}DeLong et al.^{8}
^{b}Binomial exact
Youden Index
Youden Index J 
0.9352 
95% Confidence Interval^{a} 
0.8874 to 0.9693 
Associated Criterion 
>3.8 
95% Confidence Interval^{a} 
>3.8 to >3.9 
Sensitivity 
100 
Specificity 
93.52 
Comparison of ROC curves
Variable 1 
O'sullivan test (mg/dl) 

Variable 2 
Abdominal circumference (cm) 

Variable 3 
Biparietal diameter (cm) 

Variable 4 
Femur Length (cm) 

Variable 5 
Expected fetal weight (gram) 

Variable 6 
Abdominal subcutaneous tissue fat (cm) 

Classification variable 
OGTT Diagnosis 

Sample size 
300 

Positive group: OGTT Diagnosis = 1 
7 

Negative group: OGTT Diagnosis = 0 
293 

AUC 
SEa 
95% CIb 

Osullivan_test 
0.956 
0.0404 
0.926 to 0.976 
abdominal_circumference 
0.878 
0.0615 
0.836 to 0.913 
Biparietal_diameter 
0.927 
0.0431 
0.891 to 0.954 
Femur_Length 
0.902 
0.0457 
0.863 to 0.933 
expected_fetal_weight 
0.902 
0.0511 
0.863 to 0.934 
Abdominal_subcutan_tissue_fat 
0.983 
0.00819 
0.961 to 0.994 
Youden Index
Osullivan_Test ~ Abdominal_Circumference 

Difference between areas 
0.0775 
Standard Error^{c} 
0.0836 
95% Confidence Interval 
0.0863 to 0.241 
z statistic 
0.927 
Significance level 
P = 0.3537 
Osullivan_Test ~ Biparietal_Diameter 

Difference between Areas 
0.029 
Standard Error^{c} 
0.0662 
95% Confidence Interval 
0.101 to 0.159 
z statistic 
0.438 
Significance level 
P = 0.6611 
Osullivan_Test ~ Femur_Length 

Difference between Areas 
0.0539 
Standard Error^{c} 
0.0699 
95% Confidence Interval 
0.0832 to 0.191 
z statistic 
0.77 
Significance level 
P = 0.4410 
Osullivan_Test ~ Expected_Fetal_Weight 

Difference between Areas 
0.0534 
Standard Error^{c} 
0.0735 
95% Confidence Interval 
0.0907 to 0.197 
z statistic 
0.726 
Significance level 
P = 0.4677 
Osullivan_Test ~ Abdominal_Subcutan_Tissue_Fat 

Difference between Areas 
0.0271 
Standard Error^{c} 
0.0437 
95% Confidence Interval 
0.0586 to 0.113 
z statistic 
0.619 
Significance level 
P = 0.5357 
Abdominal_Circumference ~ Biparietal_Diameter 

Difference between Areas 
0.0485 
Standard Error^{c} 
0.0289 
95% Confidence Interval 
0.00817 to 0.105 
z statistic 
1.678 
Significance level 
P = 0.0934 
Abdominal_Circumference ~ Femur_Length 

Difference between Areas 
0.0236 
Standard Error^{c} 
0.0182 
95% Confidence Interval 
0.0120 to 0.0593 
z statistic 
1.299 
Significance level 
P = 0.1939 
Abdominal_Circumference ~ Expected_Fetal_Weight 

Difference between Areas 
0.0241 
Standard Error^{c} 
0.017 
95% Confidence Interval 
0.00922 to 0.0575 
z statistic 
1.418 
Significance level 
P = 0.1561 
Abdominal_Circumference ~ Abdominal_Subcutan_Tissue_Fat 

Difference between Areas 
0.105 
Standard Error^{c} 
0.0579 
95% Confidence Interval 
0.00895 to 0.218 
z statistic 
1.806 
Significance level 
P = 0.0710 
Biparietal_Diameter ~ Femur_Length 

Difference between Areas 
0.0249 
Standard Error^{c} 
0.0181 
95% Confidence Interval 
0.0106 to 0.0603 
z statistic 
1.376 
Significance level 
P = 0.1689 
Biparietal_Diameter ~ Expected_Fetal_Weight 

Difference between Areas 
0.0244 
Standard Error^{c} 
0.0136 
95% Confidence Interval 
0.00238 to 0.0511 
z statistic 
1.786 
Significance level 
P = 0.0741 
Biparietal_Diameter ~ Abdominal_Subcutan_Tissue_Fat 

Difference between Areas 
0.0561 
Standard Error^{c} 
0.0383 
95% Confidence Interval 
0.0189 to 0.131 
z statistic 
1.465 
Significance level 
P = 0.1429 
Femur_Length ~ Expected_Fetal_Weight 

Difference between Areas 
0.000488 
Standard Error^{c} 
0.0139 
95% Confidence Interval 
0.0267 to 0.0276 
z statistic 
0.0352 
Significance level 
P = 0.9719 
Femur_Length ~ Abdominal_Subcutan_Tissue_Fat 

Difference between Areas 
0.0809 
Standard Error^{c} 
0.0421 
95% Confidence Interval 
0.00156 to 0.163 
z statistic 
1.923 
Significance level 
P = 0.0545 
Expected_Fetal_Weight ~ Abdominal_Subcutan_Tissue_Fat 

Difference between Areas 
0.0804 
Standard Error^{c} 
0.0467 
95% Confidence Interval 
0.0111 to 0.172 
z statistic 
1.723 
Significance level 
P = 0.0850 
cDeLong et al.^{8}
Table 13 Abdominal subcutaneous tissue fat (cm)
Figure 2 Box and whisker graph of gestational age (weeks), the thick line in the middle of the box represents the median, the box represents the interquartile range (from 25^{th} to 75^{th} percentiles), the whiskers represents the minimum and maximum values after excluding outliers (blackfilled circle) and extremes.
Figure 3 Box and whisker graph of O’sullivan test (mg/dl), the thick line in the middle of the box represents the median, the box represents the interquartile range (from 25^{th} to 75^{th} percentiles), the whiskers represents the minimum and maximum values after excluding outliers (blackfilled circle) and extremes.
Figure 4 Box and whisker graph of abdominal circumference (cm), the thick line in the middle of the box represents the median, the box represents the interquartile range (from 25^{th} to 75^{th} percentiles), the whiskers represents the minimum and maximum values after excluding outliers (blackfilled circle) and extremes.
Figure 5 Box and whisker graph of biparietal diameter (cm), the thick line in the middle of the box represents the median, the box represents the interquartile range (from 25^{th} to 75^{th} percentiles), the whiskers represents the minimum and maximum values after excluding outliers (blackfilled circle) and extremes.
Figure 6 Box and whisker graph of femur length, the thick line in the middle of the box represents the median, the box represents the interquartile range (from 25^{th} to 75^{th} percentiles), the whiskers represents the minimum and maximum values after excluding outliers (blackfilled circle) and extremes.
Figure 7 Box and whisker graph of expected fetal weight (gram), the thick line in the middle of the box represents the median, the box represents the interquartile range (from 25^{th} to 75^{th} percentiles), the whiskers represents the minimum and maximum values after excluding outliers (blackfilled circle) and extremes.
Figure 8 Box and whisker graph of expected abdominal subcutaneous tissue fat (cm), the thick line in the middle of the box represents the median, the box represents the interquartile range (from 25^{th} to 75^{th} percentiles), the whiskers represents the minimum and maximum values after excluding outliers (blackfilled circle) and extremes.
Figure 9 Box and whisker graph of fetal liver length (mm), the thick line in the middle of the box represents the median, the box represents the interquartile range (from 25^{th} to 75^{th} percentiles), the whiskers represents the minimum and maximum values after excluding outliers (blackfilled circle) and extremes.
Diagnostic test accuracy statistics
According to our results O’Sullivan test is a statistically significant discriminator of occurrence of gestational Diabetes mellitus with Area under the ROC curve (AUC) = 0.956 (95% Confidence interval (CI)=0.926 to 0.976) (Zstatistics=11.274, Significance level p<0.0001). This diagnostic criterion using Youden index is the level of >179 mg/dl with a sensitivity of 85.71%, specificity of 99.32%, Positive predictive value (PPV) of 75% and negative predictive value of 99.7%. Abdominal circumference is a statistically significant discriminator of occurrence of gestational Diabetes mellitus with Area under the ROC curve (AUC) =0.878. (95% Confidence interval(CI)= 0.836 to 0.913) (Zstatistics=6.148, Significance level p<0.0001). This diagnostic criterion using Youden index is the level of >20.2 cm with a sensitivity of 100.00%, specificity of 65.87 %, Positive predictive value (PPV) of 6.5% and negative predictive value of 100%. Biparietal diameter is a statistically significant discriminator of occurrence of gestational Diabetes mellitus with Area under the ROC curve (AUC) = 0.927 (95%Confidence interval(CI)=0.891 to 0.954) (Zstatistics=9.894,Significance level p<0.0001). This diagnostic criterion using Youden index is the level of >6.24 cm with a sensitivity of 85.71%, specificity of 99.2%, Positive predictive value (PPV) of 10.6% and negative predictive value of 99.7%.
Femur length is a statistically significant discriminator of occurrence of gestational Diabetes mellitus with Area under the ROC curve (AUC) = 0.902 (95% Confidence interval (CI)=0.863 to 0.933) (Zstatistics=8.795, Significance level p<0.0001). This diagnostic criterion using Youden index is the level of >4.46cm with a sensitivity of 100%, specificity of 72.35%, Positive predictive value (PPV) of 8% and negative predictive value of 100%. Expected fetal weight is a statistically significant discriminator of occurrence of gestational Diabetes mellitus with Area under the ROC curve (AUC) = 0.902 (95% Confidence interval (CI)=0.863 to 0.934) (Zstatistics=7.876, Significance level p<0.0001). This diagnostic criterion using Youden index is the level of >712 gm with a sensitivity of 100%, specificity of 67.58%, Positive predictive value (PPV) of 6.9% and negative predictive value of 100%. Abdominal subcutaneous tissue fat is a statistically significant discriminator of occurrence of gestational Diabetes mellitus with Area under the ROC curve (AUC) = 0.983 (95% Confidence interval (CI)=0.961 to 0.994) (Zstatistics=58.952, Significance level p<0.0001). This diagnostic criterion using Youden index is the level of >3.8cm with a sensitivity of 100%, specificity of 93.52%, Positive predictive value (PPV) of 26.9% and negative predictive value of 100%.
Pregnancy is a state of insulin resistance revealing subclinical defect(s) in carbohydrate metabolism that may develop into a state of carbohydrate intolerance, or gestational Diabetes Mellitus. Therefore, pregnant women must be screened for gestational Diabetes Mellitus. Uniform diagnostic criteria are lacking for more than 40 years. Our study aimed at assessing O’Sullivan test (50gram Glucose challenge test) against ultrasound measurements of abdominal circumference, biparital diameter, femur length, estimated fetal weight and abdominal subcutaneous skin fat, fetal liver length as screening for gestational diabetes mellitus between 24 and 28 weeks of gestation. The 2 hours OGTT was positive in only seven cases out of the 300 screened cases. Those positive cases were preliminary tested positive using O’sullivan test (statistically significant). In contrast, Acharya et al.^{10} studied the role of O’Sullivan test in screening of pregnant women at 2436 weeks for Gestational Diabetes. One Thousand cases were enrolled, of which only 8 cases (0.8%) were screen positive in contrast to 60 to 63 cases per 1000 in most world series. Akram et al.^{11} used GCT to screen 1000 patients with analysis of risk factors to compare the efficiency of glucose challenge test with oral glucose tolerance test for detection of gestational diabetes, 450 patients were screened with positive result and 550 patients were screened negative. Out of 450 patients with positive GCT, OGTT detected 40% patients with true positive and 50 patients with false positive results. Out of 550 GCT negative, OGTT screened 510 patients with true negative and 40 patients with false negative. So by performing OGTT 440 patients were diagnosed as gestational diabetics, while 56% had no diabetes. These results matched with ours as regards O' Sullivan test.
A range of ultrasound anthropometric parameters are used to determine normal fetal growth. In the present study we used ROC analysis to make a decision regarding fetal ultrasound parameters in predicting GDM. The present study has demonstrated that there is a highly significant correlation between fetal biparietal diameter, abdominal circumference, femur length, fetal weight, Abdominal subcutaneous tissue fat and blood glucose values during an OGTT in patients with GDM. The nature of the relationship detected implies that these parameters may be strong predictive factors for OGTT values; this was confirmed by ROC analysis. Conversely, no such relationship was found in the control group. Abdominal subcutaneous tissue fat was found to be a statistically significant discriminator of occurrence of gestational Diabetes mellitus with Area under the ROC curve (AUC) 0.983. with a sensitivity of 100%, specificity of 93.52% with regard to a cutoff value of >3.8cm, Positive predictive value (PPV) of 26.9% and negative predictive value of 100%. One of the major disadvantages of many of the screening tests used currently is falsepositive results. In the present study, Abdominal subcutaneous tissue fat measurements demonstrated a specificity near that for glucose tolerance test results based on data in the literature. Recently, studies have shown that abdominal subcutaneous tissue fat measurements, either on their own or incorporated into conventional fetal weight prediction formulae, could be used to evaluate fetal growth, and, in addition, assess whether maternal glucose levels are normal.^{12}
In a comparison of abdominal subcutaneous tissue fat thickness (ASCTT) between fetuses from a group of mothers with gestational diabetes and those from a normal control group, there were significant differences between initial fetal ASCTT, but no difference after the mothers had been treated for diabetes. The measurement of fetal ASCTT gives a more accurate estimation of the stability of maternal glucose levels than a maternal ambulatory glycemic profile.^{12} As reported, ultrasound measurements of subcutaneous adipose tissue may be a reliable indicator of the fetal metabolic state in pregnancies with GDM.^{12} Meanwhile, the availability of reference values for fetal subcutaneous fat ultrasound measurements may provide clinically useful information to identify excessive fetal fat deposition and evaluate maternal glucose levels in pregnancies with GDM, beside the routine fetal ultrasonographic biometric parameters. Comparing our results with similar studies, Vedavathi et al.^{13} studied 30 cases with an established diagnosis of gestational diabetes at 2428 weeks of gestation, by measuring abdominal circumference, head circumference and the estimated fetal weight. Abdominal circumferences (AC) of 27 (90%) cases, Head circumferences (HC) of 20 (67%) cases and estimated fetal weight (EFW) of 8 (27 %) cases were ≥90 percentile. He concluded that fetal growth parameters show significant high values in GDM. These results are criticized by the very small sample he worked upon.
In another large prospective cohort, Smith et al.^{14} concluded that excessive fetal growth preceded the diagnosis of gestational diabetes, by analysing data from 4069 pregnant women. All women provided blood samples and underwent ultrasounds at 20, 28 and 36 weeks of gestation, as well as an oral glucose tolerance test at 28 weeks. Risks were set for abdominal circumference > 90th percentile and HC/AC ratio <10th percentile. Within the cohort, 171 women (4.2%) were diagnosed with gestational diabetes at 28 weeks. Researchers found no association between fetal measurements at 20 weeks of gestation and a subsequent diagnosis of gestational diabetes; however, at 28 weeks, researchers found an increased risk for increased fetal abdominal circumference (RR = 2.05; 95% CI, 1.373.07) and decreased head circumference to abdominal circumference ratio (RR = 1.97; 95% CI, 1.32.99) in mothers with gestational diabetes. At 28 weeks, mothers with gestational diabetes had a nearly fivefold increased risk for greater fetal abdominal circumference (RR = 4.52; 95% CI, 2.986.85) and a nearly threefold increased risk for decreased head circumference to abdominal circumference ratio (RR = 2.8; 95% CI, 1.654.78). Researchers also found that increased fetal abdominal circumference was associated with a nearly fourfold increased risk for the fetus being born large for gestational age (RR = 3.86; 95% CI, 2.376.29).^{14}
Honestly we cannot criticize these results but we find them more logic than ours as the sample size was bigger and the cases were preliminary diagnosed as having gestational diabetes mellitus. Bulhing et al.^{15} studied the relationship between sonographically estimated fetal subcutaneous adipose tissue measurements and neonatal skin fold measurements in diabetic fetopathy, but his study was conducted at 37 weeks of gestation. Bulhing enrolled 172 patients (142 controls and 30 with gestational diabetes), both fetal subcutaneous fat tissue and estimated fetal weight were measured. He concluded that ultrasound examination is a reliable method for noninvasive intrauterine measurement of fetal subcutaneous tissue for predicting mechanical neonatal skinfold thickness measurements and thus gestational diabetes. Our results matched with those studies where a positive correlation was detected between fetal ultrasonographic biometric parameters including ASCTT and GDM, but we failed to find a positive correlation between fetal liver length and GDM although maternal hyperglycemia is related to fetal hyperglycemia and hyperinsulinemia, which has a significant impact on the growth of insulindependent tissues and organs, such as the liver.^{15}
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