Table 1.

PICO for study inclusion

	Population (P)	Intervention (I)	Comparison (C)	Outcomes (O)
Inclusion	Pregnant women of any age, ethnicity, socioeconomic status, geographic area, comorbidity or gestational age	Metformin administered in any form and route, alone or combined with other intervention/s, of any dosage and for any duration	Placebo, usual care and/or other pharmacological or non-pharmacological interventions including insulin, lifestyle intervention/s or other oral hypoglycaemic agents (sulfonylureas, acarbose, glibenclamide/glyburide)	Primary maternal outcomes: glycaemic control (glucose, insulin, HbA1c); incidence of GDM* and/or hyper/hypoglycaemia* Primary neonatal outcomes: hypoglycaemia*, birth weight, birth length, head circumference and gestational age at delivery Secondary outcomes: other maternal, birth and neonatal outcomes including miscarriage, birth defects, GWG, pre-eclampsia/eclampsia, LGA/macrosomia, SGA and PTB (see full list in online supplementary material)
Exclusion	Studies in non-pregnant populations	Studies without a metformin therapy arm	Studies without a control or comparison arm	Studies without clinical outcomes (mechanistic studies)
Study type		RCTs and systematic reviews of RCTs
Language		No limit
Year of publication		No limit

*As defined by authors and using the criteria selected in individual studies.

GDM, gestational diabetes mellitus; GWG, gestational weight gain; HbA1c, haemoglobin A1c; LGA, large for gestational age; PTB, preterm birth; RCT, randomised controlled trial; SGA, small for gestational age.