Cohabitation before marriage, or without it, is more common than ever- a new report from the Centers for Disease Control and Prevention (CDC) finds that couples are not only more likely to live together without getting married than in the past, they also do it for longer periods of time and, increasingly, during and after pregnancies.

The statistics present strong evidence for an enduring shift in social norms about cohabitation before marriage in the United States, suggesting that living with an unmarried partner is not only a step towards marriage, but often an alternative to it.

Researchers interviewed 12,279 American women aged 15 to 44 about cohabitation with their partners from 2006 to 2010 in the National Survey for Family Growth (NFSG), and compared the results to previous surveys.

The results showed that almost half (48 percent) of women aged 15 to 44 cohabited with a partner without being married as a "first union," compared with 43 percent in 2002 and 34 percent in 1995. Hispanic women are more likely to live with partners before marriage than any other group, and women with less education are more likely to do so than those with a college degree or higher.

They also lived with partners for a longer time without being married. The average length of cohabitation without marriage was 22 months for all women, compared to 20 months in 2002 and 13 months in 1995. Cohabitations that led to marriage also lasted longer - 21 months in the most recent period, compared to 19 months in 2002 and 14 months in 1995.

The length of cohabitation was longer for Hispanic women than any other ethnic group (33 months), and for women with less than a high school diploma (30 months) than for women with a bachelor's degree or higher (17 months).

40 percent of first premarital cohabitations led to marriage within three years, 32 percent remained intact, and 27 percent broke up. They were more likely to lead to marriage for white women and more highly educated women.

A fifth of all the women surveyed experienced a pregnancy in the first year of cohabitation, but there was a high discrepancy in education level. 33 percent of women with less than a high school diploma got pregnant during that period, compared to 5 percent of women with a college degree or higher.

"What we're seeing here is the emergence of children within cohabiting unions among the working class and the poor," said sociologist Andrew Cherlin of Johns Hopkins University to USA Today.

"They have high standards for marriage and they don't think they can meet them for now, but increasingly, it's not stopping them from having a child. Having children within cohabiting unions is much more common among everybody but the college educated."

Here are some key statistics from the women sampled from 2006 to 2010:

  • 48 percent of women cohabited as a first union, compared with 43 percent in 2002 and 34 percent in 1995.
  • Only 23 percent of women had a marriage as a first union, compared with 30 percent in 2002 and 39% in 1995.
  • Length of cohabitation before marriage: 22 months on average, up from 20 months in 2002 and 13 months in 1995
  • Race: more women cohabited as a first union across all ethnic groups, except Asian women. The 2006-2010 numbers increased to 57 percent for Hispanic women, 43 percent for white women, 39 percent for black women
  • Education: 70 percent of women with less than a high school diploma cohabited as a first union, compared to 47 percent of women with a bachelor's degree or higher.
  • Age: By age 25, 55 percent of all women aged 15-44 had ever cohabited, compared with 52 percent in 2002 and 46 percent in 1995.

The full report about trends in cohabitation before marriage is available at the Centers for Disease Control and Prevention website.