BACKGROUND: There is increasing evidence that maternal obesity is associated with several structural birth defects. Congenital abnormalities of the kidney and urinary tract (CAKUT) account for 30 to 50% of children starting kidney replacement therapy (KRT). We conducted a systematic review, meta-analysis and ecological study to explore the relationship between maternal obesity and CAKUT. METHODS: A systematic literature search was conducted in EMBASE, MEDLINE, Global Health, The Cochrane Library, Scopus and Web of Science. Study quality was assessed for bias and confounding. A meta-analysis using a random effect model was carried out to obtain a summary odds ratio (OR) and 95% confidence interval (CI). In the ecological study, country-level data were used to examine the correlation of secular trends in female obesity, CAKUT incidence and incidence of KRT. RESULTS: Eight epidemiological studies were included in the review-4 cohort studies and 4 case-control studies-7 of which were included in the meta-analysis. There was evidence of a positive association between obesity during pregnancy and the risk of CAKUT, with a summary OR = 1.14 (1.02-1.27). No association was seen with overweight, nor a dose response with increasing obesity. There was an increasing trend in countries' proportion of female obesity and an increasing trend in reported CAKUT incidence with specific rises seen in congenital hydronephrosis (CH) and multicystic kidney dysplasia (MCKD). CONCLUSIONS: Our findings suggest that pre-pregnancy obesity may be associated with increased risk of CAKUT at population level. Graphical abstract.