Iron is an essential mineral that participates in oxygen transport, DNA synthesis and repair, and as a cofactor for various cellular processes. Iron deficiency is the most common nutritional deficiency worldwide. Due to blood volume expansion and demands from the fetal–placental unit, pregnant women are one of the populations most at risk of developing iron deficiency. Iron deficiency during pregnancy poses major health concerns for offspring, including intrauterine growth restriction and long-term health complications. Although the underlying mechanisms remain unclear, maternal iron deficiency may indirectly impair fetal growth through changes in the structure and function of the placenta. Since the placenta forms the interface between mother and baby, understanding how the placenta changes in iron deficiency may yield new diagnostic indices of fetal stress in affected pregnancies, thereby leading to earlier interventions and improved fetal outcomes. In this review, we compile current data on the changes in placental development and function that occur under conditions of maternal iron deficiency, and discuss challenges and perspectives on managing the high incidence of iron deficiency in pregnant women.