Inadequate growth in utero is associated not only with adverse fetal, perinatal, and neonatal outcomes, but also with an altered propensity for disease later in life. Conversely, fetal overgrowth is also associated with increased medical risks for both mother and fetus. The interaction between the fetal genome and the intrauterine environment determines in great part how fetal growth will progress. The placental, maternal, and fetal somatotrophic axes (growth hormone/insulin-like growth factor-1) play key roles in modulating this interaction. Experimental undernutrition in animal models has numerous effects over these axes and provides insight into understanding fetal growth and its abnormalities. This review addresses the contributions made by the placental, maternal, and fetal somatotrophic axes to the regulation of fetal growth.