Death from childbirth is unusually common in America

The Economist reports:

For most of human history, pregnancy has come with a significant risk of death. Up until the early 1930s in America, nearly one woman died of related complications for every 100 live births. Thanks to advances in obstetric medicine and widened access to better care, the maternal-mortality rate declined by almost 99% over subsequent decades—one of the great public-health achievements of the 20th century. By 1987, fewer than eight women died for every 100,000 live births. Over the past quarter of a century, however, America’s maternal-mortality rate has been creeping back up

Read the article to find out some of theories behind why?