Table 1 Inclusion and exclusion criteria

• Aged 16–55

• GDM diagnosed at any gestation (typically > 12 weeks) per NICE guidelines: oral glucose tolerance test demonstrating a fasting plasma glucose level of 5.6 mmol/litre or above or a 2-h plasma glucose level of 7.8 mmol/l or above [3]

• Has commenced medication (metformin ≥ 500 mg/day) and/or insulin) within the previous 14 days

• ≤ 34 + 0 weeks of gestation

• Primiparous or multiparous

• Singleton pregnancy

• Not met NICE glucose targets with lifestyle modification of fasting glucose below 5.3 mmol/l, 1 h after meals below 7.8 mmol/l OR 2 h after meals below 6.4 mmol/l [3]

• Able to give informed consent to participate

• Aged < 16 or > 55

• Not prescribed insulin or at least 500 mg/day metformin, OR commenced medication > 14 days ago

• Met NICE glucose targets with lifestyle modification

• > 34 + 0 weeks gestation

• Chronic kidney disease

• Psychiatric inpatient treatment,

• History of bariatric surgery or other surgeries that induce malabsorption

• Long-term use (> 2 weeks) of systemic steroids within 2 weeks prior to enrolment

• Multiple pregnancy

• Unable to give informed consent to participate