The CDC4G trial : Impact of Changing Diagnostic Criteria for Gestational diabetes in Sweden – a stepped wedge national cluster randomised controlled trial-study protocol

• Introduction: In 2013 WHO recommended new criteria for GDM, defined as ≥5.1, ≥10.0 and/or ≥8.5 mmol/l fasting, 1 hour and/or 2 hour cut offs, which the Swedish National Board of Health adopted. With the current variation in GDM screening/diagnostic practice across Sweden and the debate over the criteria, we have established a stepped wedge cluster randomised controlled trial (SW-CRCT) to move towards a unified approach to GDM management. The objectives for the Changing Diagnostic Criteria for Gestational diabetes in Sweden (CDC4G) trial include: (1) To compare the rates of adverse neonatal and maternal outcomes before and after the change in GDM diagnostic criteria (2) To compare the health costs before and after the change and assess the net cost/saving (3)To compare the adverse outcomes and health costs using the new WHO criteria (75% excess risk) and the criteria based upon the 100% excess risk of neonatal adverse outcomes; using the national pregnancy register where all data needed is registered from the medical journals. The aim of this study is to describe the development of the study and the associated key issues.Methods: The CDC4G study is a national prospective, unblinded, SW-CRCT of the switch from pre-existing Swedish diagnostic criteria to the WHO 2013 criteria for GDM. Each participating centre constitutes one cluster, in which the patients undergo screening for GDM following their usual approach. The time of switch to the new criteria is randomized and subsequently rolled out until all clusters (centres) have received the intervention (introduction of the new GDM regimens) during 2018. All women treated in the participating clusters (including within primary care and hospitals) will be included in the study. Women with preexisting diabetes and overt diabetes are excluded. The key issues were identification of primary outcome, recruitment of sites and undertaking the power calculation.The study is approved by the Uppsala –Örebro regional ethics board, Dnr: 2016/487.Result: Identification of outcomes: As many women with GDM are not identified in the pre-switch period, measures that could be influenced by knowing the diagnosis (eg screening for neonatal hypoglycaemia) were excluded. The measure also needed to be frequent enough to have a large enough absolute reduction to be detected in the total obstetric population. As LGA is common (10% total population, 20% in GDM), it was decided that LGA should be primary outcome. Secondary maternal and neonate outcomes and health economic outcomes will also be evaluated. Recruitment of sites: Regions/clinics adopted the same protocols and hence were taken as ‘clusters’. There are 21 regions in Sweden and 38 clinics with annual births ranging between 540 and 10 200 births. Stockholm regions overlap so were taken as one cluster (5 clinics) . Overall 11/21 regions with 67000 births per annum agreed to participate. Annual births in Sweden is 95-100 000/year. Power calculation: With 11 clinics (clusters) participating and an intra cluster correlation of 0.0026 a minimum sample size of 47916 pregnant women (23958 before change and 23958 after change of the new GDM criteria) have 90% statistical power to detect a risk reduction of LGA by 1.5% on a population level (from 10% to 8.5%). The power calculation incorporates consideration of the varying sizes in cluster.Discussion: Establishing a national randomised controlled trial to evaluate the impact of the WHO 2013 criteria raised several challenges, which have now been addressed. The trial has commenced and final results of the study will be analyzed and disseminated in 2019 (www.cdc4g.com).Trial registration CDC4G is listed on the ISRCTN registry with study ID ISRCTN41918550 (15/12/2017).

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Endokrinologi och diabetes (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Endocrinology and Diabetes (hsv//eng)

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Reproduktionsmedicin och gynekologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Obstetrics, Gynaecology and Reproductive Medicine (hsv//eng)

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