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Introduction: Guidelines disagree on the diagnostic thresholds for gestational diabetes (GDM); treatment of women with mild fasting hyperglycemia may not be cost-effective and increase unnecessary intervention., Materials and Methods: Single-center, open-label randomized controlled feasibility trial (ISRCTN86503951). "Metformin" treatment (2 g/day) without home blood glucose monitoring (HBGM) compared to NICE "standard" diabetes prenatal care in women with fasting 5.1-5.4 mmol/L, 2H <8.5 mmol/L) at oral glucose tolerance test (OGTT)., Results: Process outcome: From the 173 women approached, 40/147 (27%) met the eligibility criteria and agreed to participate (non-completion n  = 3). All women received dietary advice. Overall, compliance was good; with the majority of women in the treatment arm reporting missing metformin tablets less than 1-3 times/week. In the treatment arm ( n  = 18), median compliance (returned packets) was 65% [0-98%]; four women were unable to tolerate the full recommended dose of metformin. All women reported being satisfied with their treatment; with 9 out of 18 women (metformin arm) reporting they would choose the same treatment in a future pregnancy however 8 women reported they would want closer prenatal monitoring. Clinical outcome: Baseline characteristics and pregnancy outcomes were not different between participants and non-participants ( n  = 133). In women randomized to the standard care arm who performed HBGM, 15/19 were prescribed metformin based on values above target despite diet and lifestyle modifications; two women required additional insulin (10%). Data on glycemic control were available for 16/19 women; a reduction in fasting and post-prandial glucose was achieved in 15/16 from recruitment to 36 weeks. There was no change in A1C in women in the treatment arm vs the standard care arm. There was no difference in the rates of LGA between participants ( n  = 40) and non-participants ( n  = 133), although there was a reduction in the median birthweight centiles in the participants, the majority of whom received metformin treatment, compared with the non-participants (35 [IQR 12-54] vs 52 [25-78]; p  = .045)., Discussion: Treatment with metformin in conjunction with routine care was acceptable to women with mild fasting hyperglycemia who participated in the trial, although overall recruitment to the study was low. Most women with mild fasting hyperglycemia (5.1-5.4 mmol/L) would meet the threshold for pharmacological treatment if identified as GDM based on current NICE guideline target blood glucose levels. However, given the low consent rate, it is unlikely that a future RCT comparing metformin treatment (in conjunction with routine prenatal care and without HBGM monitoring) to a diabetes prenatal clinic model of care would have the generalisability to inform the future management of this group.