The evidence base

The evidence base for this guideline was synthesised in accordance with SIGN methodology. Evidence was drawn from NICE clinical guideline NG3 on diabetes in pregnancy: management from preconception to the postnatal period and from a systematic review conducted by SIGN. Evidence identified by NICE covered the search range 1946–2014.

A systematic review of the literature was carried out using an explicit search strategy devised by an Information Scientist. Databases searched include Medline, Embase, Cinahl, PsycINFO and the Cochrane Library. The year range covered was 2015–2022. Internet searches were carried out on various websites for relevant evidence-based resources (NICE, GIN, TRIP, CADTH, INAHTA). The main searches were supplemented by material identified by individual members of the development group. Each of the selected papers was evaluated by two Information Scientists using standard SIGN methodological checklists before conclusions were considered as evidence by the guideline development group.

The search strategies are available on the SIGN website, www.sign.ac.uk

At the start of the guideline development process, an Information Scientist conducted a literature search for qualitative and quantitative studies that addressed patient issues of relevance to diabetes in pregnancy. Databases searched include Medline, Embase, Cinahl and PsycINFO, and the results were summarised by the SIGN Public Involvement Advisor and presented to the guideline development group.

The guideline development group identified key questions with potential cost-effectiveness implications, based on the following criteria, where it was judged particularly important to gain an understanding of the additional costs and benefits of different treatment strategies:

·     treatments which may have a significant resource impact

·     opportunities for significant disinvestment or resource release

·     the potential need for significant service redesign

·     cost-effectiveness evidence could aid implementation of a recommendation.

A systematic literature search for economic evidence for these questions was carried out by an Information Scientist covering the years 2010–2022. Databases searched include Medline, Embase and NHS Economic Evaluation Database (NHS EED). Each of the selected papers was evaluated by a Health Economist, and considered for clinical relevance by guideline group members.

Interventions are considered to be cost effective if they fall below the commonly-accepted UK threshold of £20,000 per Quality-Adjusted Life Year (QALY).

The guideline development group was not able to identify sufficient evidence to answer all of the key questions asked in this guideline (see Annex 1). The following areas for further research have been identified:

·     randomised controlled trials comparing the effectiveness of blood ketone monitoring with urine ketone monitoring for women with T1DM or T2DM during pregnancy or with GDM.

·     observational and/or mixed methods studies to investigate the optimal balance between achieving tighter blood glucose targets and avoiding hypoglycaemia to prevent adverse perinatal outcomes in women with pre-existing diabetes who are planning a pregnancy.

·     further randomised controlled trials investigating whether improvements in glucose levels linked to CGM use during pregnancy compared with SMBG is associated with reductions in adverse perinatal outcomes in women with GDM, and separately in women with T2DM.

·     randomised controlled trials comparing perinatal outcomes in pregnant women with diabetes who achieve pre-established HbA1c targets compared with pre-established glucose variability metrics (as assessed by CGM).

·     observational studies to determine the reference intervals of HbA1c in each trimester of pregnancy in healthy pregnant women in Scotland.

·     observational and/or mixed methods studies to investigate the optimal balance between achieving lower blood glucose targets and avoiding hypoglycaemia to prevent adverse perinatal outcomes in women with pre-existing diabetes during pregnancy.

·     randomised controlled trials with economic evaluations comparing outcomes in women diagnosed and treated using IADPSG 1.75 and IADPSG 2.0 criteria.

·     randomised controlled trials assessing the clinical and obstetric outcomes associated with use of current generation real-time CGM devices in women with GDM.

·     further randomised controlled trials of myo-inositol for preventing GDM, which include pregnant women of different ethnicities and varying risk factors. Myo-inositol at different doses, frequency and timing of administration should be compared with placebo, diet and exercise, and pharmacological interventions. Long-term follow up should be considered and outcomes should include potential harms, including adverse effects.

·     randomised controlled trials to investigate the most effective means of delivering dietary and other lifestyle advice, including group versus individualised delivery.

·     randomised controlled trials, or data surveillance in Scotland, to investigate outcomes of different exercise strategies in women with GDM compared with pregnant women without diabetes.

This guideline was issued in 2024 and will be considered for review in three years. The review history, and any updates to the guideline in the interim period, will be noted in the update request report, which is available in the supporting material section for this guideline on the SIGN website: www.sign.ac.uk

Comments on new evidence that would update this guideline are welcome and should be sent to the SIGN Executive, email: sign@sign.ac.uk