Final answer:
Before the twentieth century, a primary cause of maternal death was postpartum infection.
Step-by-step explanation:
The primary cause of maternal death before the twentieth century was postpartum infection. Ignaz Semmelweis, a Hungarian obstetrician in the 1840s, observed that mothers who gave birth in hospital wards staffed by doctors had a higher mortality rate from puerperal fever compared to those in wards staffed by midwives. He found that doctors were often coming directly from autopsies and carrying disease-causing matter on their hands, leading to infection in pregnant patients. Semmelweis's urging for handwashing with chlorinated lime water significantly reduced the death rate of new mothers.