Study authors Marian F. MacDorman and T.J. Mathews of the Centers for Disease Control and Prevention's National Center for Health Statistics, and Eugene Declercq of Boston University School of Public Health said out-of-hospital births include births occurring in a home, birthing center, clinic or doctor's office, or other location.
The proportion of U.S. out-of-hospital births fell to 44 percent by 1940 and dropped to 1 percent by 1969, where it remained throughout the 1980s, the study said.
The researchers used data from the CDC's National Center for Health Statistics National Vital Statistics System, Birth Data Files for 1990 to 2012, which includes data for all births occurring in the United States.
The report said, although out-of-hospital births are still rare, they began to increase in 2004 and in 2011 they rose to 1.26 percent.
In 2012, out-of-hospital births comprised 2.05 percent of births to non-Hispanic white women, 0.49 percent to non-Hispanic black women, 0.46 percent to Hispanic women, 0.81 percent to American Indian women and 0.54 percent to Asian or Pacific Islander women.
Out-of-hospital births in 2012 comprised 3 percent to 6 percent in Alaska, Idaho, Montana, Oregon, Pennsylvania and Washington; while between 2 percent and 3 percent of births outside a hospital occurred in Delaware, Indiana, Utah, Vermont and Wisconsin.
Rhode Island at 0.33 percent, Mississippi at 0.38 percent and Alabama at 0.39 percent had the lowest percentages of out-of-hospital births.