Diagnosis of gestational diabetes: Screening Test:
•ACOG recommends all pregnant women be screened at 24-28 wks of pregnancy.
•If only high risk cases are screened, 35% of gestational diabetes will not be discovered. •High risk patients are screened at 18-22 wks.
If result is negative, test should be repeated between 26-30 wks.
GCT (Glucose challenge test) :
•50g of oral glucose is given at any point during the day without regard to meal ingestion.
•A plasma glucose value of >140mg/dl at one hour is considered as GDM(Gestational diabetes mellitus) & requires OGTT with 75gm of glucose for confirmation.
•Any patient whose fasting glucose is 120mg/dl or greater is diabetic & does not need 3hrs OGTT.
OGTT(Oral glucose tolerance test): Indications:
•Glycosuria on one occasion before 20 wks.
•On >2 occasions after 20 wks. •Glycosuria at any time during pregnancy with a positive family history of diabetes.
•Past history of baby weight >4kg. •FBS >90mg/dl following a positive screening test.
Preparation:
•Unrestricted carbohydrate intake during the previous 3 days.
•Fasting for 8 hrs & not >14 hrs. •100gm (75gm according to WHO) of glucose given orally.
•Venous blood sampled at baseline and hourly for 3 hrs while continuing the fast.
Criteria for an abnormal OGTT to the diagnosis of GDM:
O' Sullivans criteria WHO(75gm) Whole blood Plasma
0 hr >90mg/dl 105mg/dl
1 hr >165mg/dl 190mg/dl
2hr >145mg/dl 165mg/dl
3hr >125mg/dl 145mg/dl
-Fasting value of >140mg/dl and after 2 hours value of > 200mg/dl in plasma is confirmative of GDM.
-If 2 or more values are abnormal patient is diagnosed as GDM.
-If only 1 value is abnormal,cannot be diagnosed as GDM, but the patient is at risk for macrosomia around 20%, and for preeclampsia & eclampsia 7.9%.
Repeat testing should be done.
-With no abnormal values patients have a risk for macrosomia 6.6%, preeclampsia & eclampsia 3.3%.
-Even those with normal 3 hr GTT after an abnormal screening test are at risk for macrosomia.
•Urine glucose is not used as standard test because the renal glucose threshold decreases during normal gestation leading to glycosuria.
•HbA1c is not used as screening test because of the length of the time that is required to increase the percentage of glycosylation of the hemoglobin molecule.
•ACOG recommends all pregnant women be screened at 24-28 wks of pregnancy.
•If only high risk cases are screened, 35% of gestational diabetes will not be discovered. •High risk patients are screened at 18-22 wks.
If result is negative, test should be repeated between 26-30 wks.
GCT (Glucose challenge test) :
•50g of oral glucose is given at any point during the day without regard to meal ingestion.
•A plasma glucose value of >140mg/dl at one hour is considered as GDM(Gestational diabetes mellitus) & requires OGTT with 75gm of glucose for confirmation.
•Any patient whose fasting glucose is 120mg/dl or greater is diabetic & does not need 3hrs OGTT.
OGTT(Oral glucose tolerance test): Indications:
•Glycosuria on one occasion before 20 wks.
•On >2 occasions after 20 wks. •Glycosuria at any time during pregnancy with a positive family history of diabetes.
•Past history of baby weight >4kg. •FBS >90mg/dl following a positive screening test.
Preparation:
•Unrestricted carbohydrate intake during the previous 3 days.
•Fasting for 8 hrs & not >14 hrs. •100gm (75gm according to WHO) of glucose given orally.
•Venous blood sampled at baseline and hourly for 3 hrs while continuing the fast.
Criteria for an abnormal OGTT to the diagnosis of GDM:
O' Sullivans criteria WHO(75gm) Whole blood Plasma
0 hr >90mg/dl 105mg/dl
1 hr >165mg/dl 190mg/dl
2hr >145mg/dl 165mg/dl
3hr >125mg/dl 145mg/dl
-Fasting value of >140mg/dl and after 2 hours value of > 200mg/dl in plasma is confirmative of GDM.
-If 2 or more values are abnormal patient is diagnosed as GDM.
-If only 1 value is abnormal,cannot be diagnosed as GDM, but the patient is at risk for macrosomia around 20%, and for preeclampsia & eclampsia 7.9%.
Repeat testing should be done.
-With no abnormal values patients have a risk for macrosomia 6.6%, preeclampsia & eclampsia 3.3%.
-Even those with normal 3 hr GTT after an abnormal screening test are at risk for macrosomia.
•Urine glucose is not used as standard test because the renal glucose threshold decreases during normal gestation leading to glycosuria.
•HbA1c is not used as screening test because of the length of the time that is required to increase the percentage of glycosylation of the hemoglobin molecule.
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