More than a quarter of the unmarried women who gave birth in a recent year were living with a partner, according to a Census Bureau report that for the first time measured the percentage of unmarried mothers who were not living alone.
"Everybody tends to think of single mothers as being alone with their child, and we wanted to look at whether that was true," said Jane Dye, the demographer who wrote the report, "Fertility of American Women: 2008." "We found that 28 percent of these women were living with an unmarried partner, whether opposite sex or same sex."
While cohabitation has increased enormously over the last generation, the catchall category of "single mother" has often blurred the difference between those living alone and those living with a partner.
But recently, the Census Bureau's Current Population Survey, one of the sources for the fertility report, added a question on cohabitation to make it possible to measure how many new mothers were actually on their own.
Cohabitation is now widely used as a transitional stop en route to marriage. A February National Center for Health Statistics study said about half of cohabiting couples marry within three years, and about two-thirds within five.
Pamela J. Smock, director of the Population Studies Center at the University of Michigan, said many people delayed marriage until they had achieved a basic level of economic security.
"Economic situations really matter for people getting married," she said. "Many people say they will not get married unless they can have a wedding and a savings account, but they might have a child in a cohabiting relationship. That's become almost a mainstream way of starting a family, with less stigmatization than even 10 years ago."
Andrew Cherlin, a Johns Hopkins University demographer, and Smock said they were surprised the number of mothers living with partners was not higher, since earlier estimates put it at around half of unmarried mothers.
"Cohabitation until recently was invisible in government reports," Cherlin said. "It's data we need. If we're concerned about stable environments for children, we have to know whether we should be focusing our efforts on helping cohabiting couples keep their relationship together, or whether we're talking about unmarried teen mothers who are on their own."
According to the Census Bureau report, released Thursday, unmarried women made up 1.5 million of the 4 million women ages 15 to 44 who gave birth between June 2007 and June 2008.
The report also found that the proportion of mothers of newborns who were in the labor force had increased to 61 percent in 2008, from 57 percent in 2006. Similar studies have shown that the percentage of working mothers with newborns rose to a peak of 59 percent in 1998 and then declined, but that it has lately been rising close to peak levels.
Nationwide, the report found, 6 percent of mothers with newborns were unemployed but looking for work in 2008, down from 6.9 percent in two years earlier.
"With the recession, it seems like new mothers are pitching in and working when they otherwise might not," Dye said.
Nationally, one in four mothers who recently gave birth lived in poverty in 2008. About 20 percent of the women who gave birth during the year were foreign-born, the report found.