Gestational diabetes can be reliably detected with a sugar tolerance test. Therefore, the test is recommended as part of the mother-child pass examinations for all pregnant women between the 24th and 28th week of pregnancy, and possibly earlier if risk factors for diabetes are present.
The test can be carried out at the family doctor or in a laboratory, the costs for which are covered by the health insurance company. Taking the test is a prerequisite for receiving full childcare allowance.
In order to be able to carry out the test and to obtain a meaningful result, certain conditions should be met. The pregnant woman should.
- Do not have any acute illness at the time of the examination (e.g. fever, nausea or vomiting during pregnancy).
- Do not change their normal eating and drinking habits in the three days prior to the examination
- Do not exert yourself physically before the test
- Do not eat anything from around 10 p.m. on the evening before the examination (a fasting period of at least 8 hours is recommended)
- Do not take any medication that interferes with the insulin balance on the morning of the examination.
Procedure of the Investigation
The test should be done in the morning. The fasting blood sugar level is measured immediately before the start of the test. For this purpose, blood is drawn from the vein and the glucose concentration in the venous plasma is determined.
Then the pregnant woman is given 300 ml of water in which 75 g of glucose has been dissolved to drink (this is why the test is also known as 75 g oGTT). After one and two hours after drinking the solution, the blood sugar level is determined again – a total of three blood samples are necessary.
The pregnant woman has to plan around two hours for the test. In the waiting time between the sugar measurements she should stay near the test laboratory, not move unnecessarily or physically exert yourself and no other examinations should be carried out during this period. In addition, nothing may be eaten in the waiting time between measurements.
The blood sugar level should always be measured from venous plasma as part of the sugar stress test. The determination of the blood sugar level by a small prick in the fingertip (capillary whole blood) is not reliable for the diagnosis of gestational diabetes, since all limit values refer to venous plasma.
Evaluation of Results
The following blood sugar values from venous plasma are the limit values for the diagnosis of gestational diabetes:
- On an empty stomach (before drinking the glucose solution) 92 mg/dl
- One hour after drinking the solution 180 mg/dl
- Two hours after drinking the solution 153 mg/dl
The diagnosis “gestational diabetes” can be made as soon as one of these three values is exceeded.
Differentiation Between Gestational Diabetes and Manifest Diabetes
The distinction between gestational diabetes and manifest diabetes is based on the level of blood sugar.
When measuring the fasting blood sugar level, the following limit values apply:
- Normal value 92 mg/dl
- Gestational diabetes 92-125 mg/dl
- Suspected overt diabetes mellitus 126 mg/dl
If the fasting blood sugar value exceeds 126 mg/dl, manifest diabetes mellitus is suspected. In this case, the value must be checked in a second examination, that is, the fasting blood sugar must be determined again.