Some trends are harder to explain than others. Home births, for example. They are increasing.
A century ago, most babies in the United States were born outside a hospital, the vast majority at home. The number steadily declined to about 1 percent in the late 1960s, where it stayed for decades. More-specific wording on birth certificates picked up a continuing decline, from 0.69 percent in 1989 to 0.56 percent in 2004.
After 15 years, the trend reversed, rising to 0.67 percent in 2008 - a tiny difference, to be sure, but those 5,207 additional born-at-home babies contributed to a statistically significant jump of 20 percent in four years.
Even more interesting is who they were: Almost all the increase was due to white women (0.80 percent of births at home in 2008). Black women declined slightly (to 0.28 percent); Hispanics were unchanged (0.20 percent).
And where they lived: Pennsylvania, where 1.54 percent of all births were residential, was among the top six home-born states; New Jersey, with 0.26 percent, was among the bottom six. The reason for the disparity is unclear, although the Keystone State's vast rural areas and larger Amish population might play a role.
The new analysis, published online Friday in the journal Birth: Issues in Perinatal Care, noted that the U.S. is typical of most industrialized countries with fewer than 1 percent of births at home. There are exceptions: 30 percent of babies in the Netherlands are home-delivered; in England, the rate nearly tripled, from 1 percent in 1983 to 2.9 percent in 2008.
So what is going on?
Although the American Public Health Organization and some other groups support home births, influential organizations, like the American College of Obstetricians and Gynecologists, cite safety concerns and oppose them. And Caesarean sections, the polar opposite of a typical midwife-assisted, in-your-own-bed home birth, are at record levels.
That could be a clue.
"Maybe some women have become sort of uncomfortable with what happens in a hospital, high C-section rates, medical intervention, things like that," speculated Marian MacDorman, the new paper's lead author and a statistician at the National Center for Health Statistics.
Check out more Check Up items.