Abstract: Background The International Association of Diabetes and Pregnancy Study Groups (IADPSG) recommends universal screening with a 75 g oral glucose tolerance test (OGTT) using stricter criteria for gestational diabetes (GDM). This may lead to important increases in the prevalence of GDM and associated costs, whereas the gain in health is unclear. The goal of The Belgian Diabetes in Pregnancy Study (BEDIP-N) is to evaluate the best screening strategy for pregestational diabetes in early pregnancy and GDM in an ethnically diverse western European population. The IADPSG screening strategy will be followed, but in addition risk questionnaires and a 50 g glucose challenge test (GCT) will be performed, in order to define the most practical and most cost effective screening strategy in this population. Methods BEDIP-N is a prospective observational cohort study in 6 centers in Belgium. The aim is to enroll 2563 pregnant women in the first trimester with a singleton pregnancy, aged 1845 years, without known diabetes and without history of bariatric surgery. Women are universally screened for overt diabetes and GDM in the first trimester with a fasting plasma glucose and for GDM between 2428 weeks using the 50 g GCT and independently of the result of the GCT, all women will receive a 75 g OGTT using the IADPSG criteria. Diabetes and GDM will be treated according to a standardized routine care protocol. Women with GDM, will be reevaluated three months postpartum with a 75 g OGTT. At each visit blood samples are collected, anthropometric measurements are obtained and self-administered questionnaires are completed. Recruitment began in April 2014. Discussion This is the first large, prospective cohort study rigorously assessing the prevalence of diabetes in early pregnancy and comparing the impact of different screening strategies with the IADPSG criteria on the detection of GDM later in pregnancy.