Until the early decades of the 20th century, women spent more than 60% of their prime-age years either pregnant or nursing. Since then, the introduction of infant formula reduced women's comparative advantage in infant care, by providing an effective breast milk substitute. In addition, improved...

Maternal mortality was the second-leading cause of death for women in childbearing years up until the mid-1930s in the United States. For each death, twenty times as many mothers were estimated to suffer pregnancy-related conditions, often leading to severe and prolonged disablement. Poor...