Worldwide, women suffer an estimated 2.65 million stillbirths each year. Despite those huge numbers, we only understand some of the factors that are responsible. In low- and middle-income countries (where most of the world’s stillbirths occur), diseases like malaria can put pregnant women at risk of stillbirths. In wealthier countries, the biggest risks include smoking and obesity. But these factors only go partway to explaining why some women have stillbirths, leaving many cases unaccounted for. The benefits that would come from that knowledge could be enormous.

One way to learn about reproductive health is to observe how our primate cousins have babies. And a new study on marmosets offers some hints about the causes of stillbirth. It suggests that a mother’s health during