The incarceration rate in the United States is the highest of any country in the world, with more than two million people currently imprisoned. Mass incarceration is not unique to men—the nation also holds nearly a third of the world’s incarcerated female population. Overall, the total U.S. prison population has declined by 17% since 2009; however, this was driven by a decrease in male incarceration, while some states saw an increase in female incarceration. The most recent estimates show that more than 223,000 women are incarcerated in jails and prisons in the United States, and an estimated 3–4% of these women are pregnant on entry.