The General hypothesis is that the IADPSG screening strategy for gestational diabetes (GDM) will lead to an important increase in the work load and the prevalence of GDM in Belgium but that this might not be cost effective concerning the prevention of adverse pregnancy outcomes. The risk to develop type 2 diabetes postpartum will probably be lower than for women diagnosed with the two-step screening strategy.

In this prospective multicentric cohort study, women will be universally screened for pregestational diabetes and GDM at the first prenatal visit during the first trimester by measuring the fasting plasma glucose. In the second trimester, women without diagnosis of diabetes or GDM in the first trimester, will be universally screened for GDM using the 50g glucose challenge test (GCT) and the 75g oral glucose tolerance test (OGTT) with the IADPSG criteria for GDM. Diagnosis of GDM will be based on the 75g OGTT.

Accurate data on the prevalence of gestational diabetes (GDM) are lacking in Belgium and the current practice for screening for GDM varies across different centers. The discrepancy in recommendations is due to the lack of data based on research in our population concerning the best screening strategy for pregestational diabetes in early pregnancy and the lack of data on the best screening strategy for GDM. A substantial number of centers in Belgium already use the IADPSG screening strategy although not always a an universal screening strategy or not always as an one-step screening strategy.

The General hypothesis is that the IADPSG screening strategy will lead to an important increase in the work load and the prevalence of GDM in Belgium but that this might not be cost effective concerning the prevention of adverse pregnancy outcomes. The risk to develop type 2 diabetes postpartum will probably be lower than for women diagnosed with the two-step screening strategy.

In this prospective cohort study, women will be universally screened for pregestational diabetes and GDM at the first prenatal visit during the first trimester by measuring the fasting plasma glucose. GDM will be defined as a fasting plasma glucose ≥100-125mg/dl. This will allow to identify the most important risk factors for the development of GDM.

In the second trimester, women will be universally screened for GDM using the 50g glucose challenge test (GCT) and the 75g oral glucose tolerance test (OGTT)with the IADPSG criteria for GDM. Compared to the IADPSG screening strategy used in normal routine, the 50g GCT will be an extra test specific for the study. Diagnosis of GDM will be based on the 75g OGTT. Participants and researchers will therefore be blinded for the result of the GCT. The results of the GCT test will be used at the end of the study for research purposes only. The use of a GCT as an universal screening tool in a two-step approach with the use of the 75g 2-hour OGTT with the IADPSG criteria only if the GCT is abnormal, is not yet validated and will be evaluated in the study, since this could be a practical solution. Differences in GDM prevalence and pregnancy outcomes will be analyzed using different diagnostic criteria based on the 75g OGTT: the Carpenter & Coustan criteria, the IADPSG criteria, and threshold values if diagnostic criteria would be based on an odds ratio of 2.0. The evaluation of different screening strategies and different diagnostic criteria will allow to explore the most cost effective methods for identifying women at risk for adverse pregnancy outcomes and at high risk for the development of type 2 diabetes after pregnancy. By using a multivariable risk estimation model based on the most relevant clinical risk factors and biochemical measures for GDM in our own population, the aim is to develop a simple and cost effective screening algorithm.

This study will also allow to evaluate the best short-term follow up strategy postpartum for women with a previous history of GDM. Different screening tests will be used three months postpartum: a fasting plasma glucose, Hba1c and 75g OGTT.

Inclusion Criteria:

• Women between 18-45 years,
• singleton pregnancy
• between 6-13 weeks of pregnancy
• the delivery has to be planned in the hospital where the study is performed.

Exclusion Criteria:

• < 18 years or > 45 year
• multiple pregnancy
• known diabetes or taking metformin
• chronic treatment with corticoids
• signs of a miscarriage
• Chronic medical condition: uncontrolled hypertension, severe heart disease, severe chronic liver disease, severe chronic kidney disease, chronic infection (such as HIV or hepatitis)
• bariatric surgery
• delivery is planned in another center than the screening
• a normal follow up and treatment during pregnancy will not be possible (due to incompliance, psychiatric problems, severe communication problems…)
• participating in another study with any medication or intervention ( including life style intervention) up to 90 days before the start of the study

Pregnant women without known diabetes attending a first prenatal visit in obsetrical centers, both in university and in non-university hospitals