Pregnant women infected with malaria have lower levels of an essential amino acid called L-arginine, which may help to explain why these women are more likely to experience complications such as stillbirths and low birth weight infants. Malaria infection in pregnancy (MIP) is a leading cause of maternal-child morbidity and mortality worldwide, and as such reducing adverse birth outcomes is a global health priority - yet few safe and effective interventions exist. Here, Chloe McDonald and colleagues found that low levels of L-arginine in a group of 384 pregnant women in Malawi were associated with worse pregnancy outcomes. Working in pregnant mice, the researchers observed that those infected with malaria benefited from L-arginine supplementation, increasing viability and birth weights among the pups delivered. They found the amino acid plays a key role in the synthesis of nitric oxide, which guides the development of blood vessels in the placenta. McDonald et al. used imaging of the pregnant mice with malaria to confirm how L-arginine supplementation reduces inflammation and prompts vascular development in the placenta. Each year, about 125 million women become pregnant in regions where malaria is endemic and where diets are poor in L-arginine. In a related Focus, James Beeson and colleagues discuss the "potential simplicity, affordability and practicality" of amino acid supplementation for these women. The study authors say that novel interventions aimed at promoting placental function may improve birth outcomes not only for MIP, but also for other causes of adverse pregnancy outcomes associated with placental insufficiency.