In all, 1,702 unselected pregnant women from the city of La Plata were tested for gestational diabetes mellitus (GDM) and evaluated to determine GDM prevalence and risk factors. In women with GDM, we evaluated compliance with guidelines for GDM management, and perinatal complications attributable to GDM. GDM prevalence was 5.8%, and its risk factors were pre-gestational obesity, previous hyperglycaemia, age > 30 years, previous GDM (and its surrogate markers). In primi-gravida (PG) subjects, GDM was equally prevalent in the presence (4.2%) or absence (4.0%) of risk factors. In multi-gravida (MG) women, although risk factors doubled the prevalence of GDM (8.6%), in the absence of risk factors GDM prevalence was similar to that of PG women (3.9%). Half of all women with GDM received inadequate post-diagnosis obstetric control, and this induced a fourfold increase in infant perinatal complications. In conclusion, all non-hyperglycaemic 24-28-week pregnant women should be tested for GDM, although particular attention must be paid to MG women with risk factors.