The incidence of obesity is rising, which lowers patient quality of life and raises societal health care expenses. Obesity is characterised by an excessive accumulation of fats in the body; significantly raises the risk of a number of diseases including diabetes, cardiovascular diseases and fatty liver disease (non-alcoholic); and is associated with a shorter life span. Emerging evidence highlights the critical role of the intrauterine environment in programming metabolic pathways that influence obesity risk later in life of offspring. Maternal factors such as diet, gestational weight gain, metabolic health and exposure to environmental toxins can profoundly impact foetal growth and adiposity. Furthermore, gestational diabetes and maternal obesity are strongly associated with changes in foetal body composition and the development of obesity. Therefore, here we summarize the many prenatal determinants of obesity, investigating crucial components such as maternal metabolic health, dietary imbalances and environmental exposures. Understanding the prenatal causes of obesity is critical for guiding public health policy and devising targeted interventions to minimise the obesity burden across generations.