Characteristics of included studies. Table Abbreviations: RCT = randomised controlled trial, IV = intravenous, GDM = gestational diabetes mellitus, PIH = pregnancy induced hypertension, PROM = premature rupture of membranes, REEDA = redness, edema, ecchymosis, discharge and approximation of wound edges, OASI = obstetric anal sphincter injury, HIV = human immunodeficiency virus, IBD = inflammatory bowel disease, PPROM = preterm premature rupture of membranes, PPH = postpartum haemorrhage, DM = diabetes mellitus, Hb = haemoglobin, HTN = hypertension, VAS = visual analogue scale. Here, GSTM1 is linked to spontaneous preterm birth.